Decreased kidney function of unknown cause in Nicaragua: a community-based survey

The Utility of Novel Renal Biomarkers in Assessment of Chronic Kidney Disease of Unknown Etiology (CKDu): A Review

Chronic Kidney Disease (CKD) is a globally prevalent non-communicable disease with significant mortality and morbidity. It is typically associated with diabetes and hypertension; however, over the last two decades, an emergence of CKD of unknown etiology (CKDu) has claimed thousands of lives in several tropical agricultural communities. CKDu is associated with gradual loss of renal function without initial symptoms until reaching complete kidney failure and eventually death. The most impacted are young adult males of lower socio-economic strata. Since the disease progression can be successfully attenuated through early detection, the development of superior screening and management measures is of utmost importance. In contrast to the conventional biomarkers, novel biomarkers with improved sensitivity and specificity are being discussed as promising tools for early diagnosis of the disease. This review summarizes emerging novel biomarkers used in assessing CKD and discusses the current utility and diagnostic potential of such biomarkers for CKDu screening in clinical settings of different communities impacted by CKDu. Our goal is to provide a framework for practitioners in CKDu impacted regions to consider the use of these novel biomarkers through this synthesis. The increased use of these biomarkers will not only help to validate their diagnostic power further and establish potential prognostic value but may also provide critical insights into sites and mechanisms of renal damage.

Evidence of nickel and other trace elements and their relationship to clinical findings in acute Mesoamerican Nephropathy: A case-control analysis

Background

Although there are several hypothesized etiologies of Mesoamerican Nephropathy (MeN), evidence has not yet pointed to the underlying cause. Exposure to various trace elements can cause the clinical features observed in MeN.

Methods and findings

We measured 15 trace elements, including heavy metals, in renal case-patients (n = 18) and healthy controls (n = 36) in a MeN high-risk region of Nicaragua. Toenails clippings from study participants were analyzed using inductively coupled plasma mass spectrometry. A case-control analysis was performed, and concentrations were also analyzed over participant characteristics and clinical parameters. Nickel (Ni) concentrations were significantly higher in toenails from cases (1.554 mg/kg [0.176–42.647]) than controls (0.208 mg/kg [0.055–51.235]; p<0.001). Ni concentrations correlated positively with serum creatinine levels (p = 0.001) and negatively with eGFR (p = 0.001). Greater Ni exposure was also associated with higher leukocyte (p = 0.001) and neutrophil (p = 0.003) counts, fewer lymphocytes (p = 0.003), and lower hemoglobin (p = 0.004) and hematocrit (p = 0.011).

Conclusions

Low-dose, chronic environmental exposure to Ni is a possible health risk in this setting. Ni intoxication and resulting systemic and renal effects could explain the clinical signs observed during early MeN. This study provides compelling evidence for a role of Ni in the acute renal impairment observed in this MeN high-risk population. Additional work to assess exposure levels in a larger and heterogeneous population, identify environmental sources of Ni and exposure pathways, and evaluate the link between Ni and MeN pathogenesis are urgently needed.

Kidney Function, Self-Reported Symptoms, and Urine Findings in Nicaraguan Sugarcane Workers

Background

An epidemic of CKD in Central America predominantly affects males working in certain industries, including sugarcane. Urinary tract infections are commonly diagnosed among men in Nicaragua, who often receive antibiotics and nonsteroidal anti-inflammatory drugs for urinary symptoms.

Methods

We followed 251 male Nicaraguan sugarcane workers in seven job tasks over one harvest and measured urine dipstick parameters, kidney injury biomarkers, and eGFR. We administered a questionnaire about urinary symptoms, health-related behaviors, and medication history. We cultured urine in a subset of workers.

Results

The study population was composed of factory workers (23%), cane cutters (20%), irrigators (20%), drivers (16%), agrichemical applicators (12%), seeders/reseeders (6%), and seed cutters (4%). The mean age of participants was 33.9 years, and mean employment duration was 10.1 years. Cane cutters reported higher proportions of urinary-related symptoms compared with agrichemical applicators, irrigators, and seeders/reseeders. Seed cutters were more likely to take antibiotics (22%), whereas drivers and seeders/reseeders were more likely to take pain medications (27% and 27%, respectively). Proteinuria was uncommon, whereas dipstick leukocyte esterase was relatively common, especially among cane cutters, seed cutters, and seeders/reseeders (33%, 22%, and 21% at late harvest, respectively). Dipstick leukocyte esterase at late harvest was associated with a 12.9 ml/min per 1.73 m2 (95% CI, -18.7 to -7.0) lower mean eGFR and 2.8 times (95% CI, 1.8 to 4.3) higher mean neutrophil gelatinase-associated lipocalin. In general, workers who reported urinary-related symptoms had higher mean kidney injury biomarker levels at late harvest. None of the workers had positive urine cultures, including those reporting urinary symptoms and/or with positive leukocyte esterase results. Amoxicillin, ibuprofen, and acetaminophen were the most commonly used medications.

Conclusions

Job task is associated with urinary symptoms and dipstick leukocyte esterase. Urinary tract infection is misdiagnosed based on leukocyte esterase, which may be an important predictor of kidney outcomes.

Occupational risk factors for chronic kidney disease in Andhra Pradesh: 'Uddanam Nephropathy'

BACKGROUND

CKD of unknown etiology (CKDu) has been reported in several countries including India. We previously showed a prevalence of CKD in India to be 17.2% and we found a CKD epidemic in Andhra Pradesh (AP) to be 46.8%. We conducted this study to further explore the unexplained CKD epidemic in AP.

METHODS

We recruited 1201 adult participants through systematic random sampling from eight administrative divisions. Demographic, medical, and detailed occupational history was collected. Anthropometric measurements and blood pressure were taken and blood and urine samples were collected. Poisson regression model was used to identify potential predictors for CKD.

RESULTS

We analyzed data for 1184 individuals with mean age of 44.6 ± 14.0 years, of whom 44% were male. Prevalence of CKD was 32.2%. Working as a farmer had 20% more prevalence of CKD compared to non-farmers in the fully adjusted model (PR 1.2, 95% CI 1.01-1.42). Age, alcohol consumption, and chewing tobacco were also independent predictors of CKD. Gender, hypertension, and diabetes were not associated with CKD.

CONCLUSIONS

The prevalence of CKD in AP is 32.2%. Occupational exposure among farmers could play a potential role in this epidemic. Large longitudinal epidemiologic research studies are needed to trace the causes of this problem.

Prevalence and risk factors for chronic kidney disease of unknown cause in Malawi: a cross-sectional analysis in a rural and urban population

BACKGROUND

An epidemic of chronic kidney disease of unknown cause (CKDu) is occurring in rural communities in tropical regions of low-and middle-income countries in South America and India. Little information is available from Southern African countries which have similar climatic and occupational characteristics to CKDu-endemic countries. We investigated whether CKDu is prevalent in Malawi and identified its potential risk factors in this setting.

METHODS

We conducted a cross-sectional study from January-August 2018 collecting bio samples and anthropometric data in two Malawian populations. The sample comprised adults > 18 years (n = 821) without diabetes, hypertension, and proteinuria. Estimates of glomerular filtration rate (eGFR) were calculated using the CKD-EPI equation. Linear and logistic regression models were applied with potential risk factors, to estimate risk of reduced eGFR.

RESULTS

The mean eGFR was 117.1 ± 16.0 ml/min per 1.73m2 and the mean participant age was 33.5 ± 12.7 years. The prevalence of eGFR< 60 was 0.2% (95% confidence interval (95% CI) 0.1, 0.9); the prevalence of eGFR< 90 was 5% (95% CI =3.2, 6.3). We observed a higher prevalence in the rural population (5% (3.6, 7.8)), versus urban (3% (1.4, 6.7)). Age and BMI were associated with reduced eGFR< 90 [Odds ratio (OR) (95%CI) =3.59 (2.58, 5.21) per ten-year increment]; [OR (95%CI) =2.01 (1.27, 3.43) per 5 kg/m2 increment] respectively. No increased risk of eGFR < 90 was observed for rural participants [OR (95%CI) =1.75 (0.50, 6.30)].

CONCLUSIONS

Reduced kidney function consistent with the definition of CKDu is not common in the areas of Malawi sampled, compared to that observed in other tropical or sub-tropical countries in Central America and South Asia. Reduced eGFR< 90 was related to age, BMI, and was more common in rural areas. These findings are important as they contradict some current hypothesis that CKDu is endemic across tropical and sub-tropical countries. This study has enabled standardized comparisons of impaired kidney function between and within tropical/subtropical regions of the world and will help form the basis for further etiological research, surveillance strategies, and the implementation and evaluation of interventions.

CKDNET, a quality improvement project for prevention and reduction of chronic kidney disease in the Northeast Thailand

BACKGROUND

The incidence of chronic kidney disease (CKD) is high in the Northeast Thailand compared to other parts of the country. Therefore, a broad program applying all levels of care is inevitable. This paper describes the results of the first year trial of the Chronic Kidney Disease Prevention in the Northeast Thailand (CKDNET), a quality improvement project collaboratively established to curb CKD.

METHODS

We have covered general population, high risk persons and all stages of CKD patients with expansive strategies such as early screening, effective CKD registry, prevention and CKD comprehensive care models including cost effectiveness analysis.

RESULTS

The preliminary results from CKD screening in general population of two rural sub-districts show that 26.8% of the screened population has CKD and 28.9% of CKD patients are of unknown etiology. We have established the CKD registry that has enlisted a total of 10.4 million individuals till date, of which 0.13 million are confirmed to have CKD. Pamphlets, posters, brochures and other media of 94 different types in the total number of 478,450 has been distributed for CKD education and awareness at the community level. A CKD guideline that suits for local situation has been formulated to deal the problem effectively and improve care. Moreover, our multidisciplinary intervention and self-management supports were effective in improving glomerular filtration rate (49.57 versus 46.23 ml/min/1.73 m2; p < 0.05), blood pressure (129.6/76.1 versus 135.8/83.6 mmHg) and quality of life of CKD patients included in the program compared to those of the patients under conventional care. The cost effectiveness analysis revealed that lifetime cost for the comprehensive health services under the CKDNET program was 486,898 Baht compared to that of the usual care of 479,386 Baht, resulting in an incremental-cost effectiveness ratio of 18,702 Baht per quality-adjusted life years gained.

CONCLUSION

CKDNET, a quality improvement project of the holistic approach is currently applying to the population in the Northeast Thailand which will facilitate curtailing of CKD burden in the region.

Estimated plasma osmolarity and risk of end-stage kidney disease in patients with IgA nephropathy

BACKGROUND

Several experimental studies have indicated that increased plasma osmolarity caused by recurrent dehydration is involved in kidney injury via a mechanism, mediated by vasopressin secretion and activation of the aldose reductase pathway. Epidemiologic evidence linking increased plasma osmolarity and the onset of end-stage kidney disease (ESKD), in patients with primary glomerulonephritis, is lacking.

METHODS

We retrospectively examined 663 patients with IgA nephropathy (IgAN) diagnosed by kidney biopsy and evaluated the association between estimated plasma osmolarity and ESKD prevalence, using a Cox proportional hazards model.

RESULTS

During follow-up (median 80.4 months; interquartile range 22.2-120.1), 73 patients developed ESKD. In a baseline survey, plasma osmolarity was correlated negatively with the mean value of the estimated glomerular filtration rate, but correlated positively with the mean value of urinary protein excretion, systolic blood pressure, and pathologic severity of extracapillary proliferation, in addition to tissue fibrosis and sclerosis. The incidence rate of ESKD increased linearly with increase in plasma osmolarity (P < 0.05 for trend). In multivariate analyses, plasma osmolarity was an independent risk factor for ESKD (hazard ratio for each increment of 5 mOsm/kg in plasma osmolarity 1.56; 95% confidence interval 1.18-2.07) even after adjustment for potential confounders.

CONCLUSIONS

Increased plasma osmolarity was associated significantly with an increased risk of ESKD in patients with IgAN. Maintenance of plasma osmolarity by appropriate control of the balance between salt and water may contribute to kidney protection.

Risk of kidney stone among workers exposed to high occupational heat stress - A case study from southern Indian steel industry

BACKGROUND

Predicted temperature rise is likely to increase the risks of development and progression of renal/urologic anomalies for workers engaged in physically exerting and high-heat occupations.

METHODS

We conducted a cross-sectional study with 340 steelworkers engaged in moderate to heavy labour with ≥3 year's heat exposures and assessed Wet Bulb Globe Temperature (WBGT) and heat-strain indicators. We captured self-reported heat-strain and kidney symptoms using validated questionnaires and subjected 91 workers to renal ultrasound upon referral of an occupational health specialist to detect and confirm any structural renal anomalies/stones.

RESULTS

The results show that heat exposures (Avg.WBGT = 33.2 °C ± 3.8 °C) exceeded the Threshold Limit Value (TLV) for 220 workers. 95% of the workers reported symptoms of heat strain and dehydration and significant associations between heat exposures, rise in Core Body Temperature (CBT) (p = 0.0001) and Urine Specific Gravity (USG) (p = 0.018) were observed. Of the 91 workers subjected to renal ultrasound, 33% were positive for kidney/ureteral stones (n = 25) & other structural renal anomalies (n = 5). Renal/urologic anomalies were higher in the heat-exposed workers (AOR = 2.374; 95% C.I = 0.927 to 6.077; p = 0.072) 29% of workers were from exposed group and 4% were from unexposed group. Years of exposure to heat (≥5 vs <5) were significantly associated with the risk of renal anomalies/calculi.

CONCLUSION

The preliminary finding concludes that high-heat stress combined with a heavy workload and chronic dehydration are high-risk factors for adverse renal health and calls for the urgent need for cooling interventions, enhanced welfare facilities, and protective labour policies to avert adverse health consequences for few million workers in the climate change scenario.

Prevalence and Risk Factors for CKD in the General Population of Southwestern Nicaragua

BACKGROUND

Studies have described Mesoamerican nephropathy among agricultural workers of El Salvador and northwestern Nicaragua. Data on prevalence and risk factors for CKD beyond agricultural workers and in other regions in Nicaragua are sparse.

METHODS

We recruited participants from 32 randomly selected communities in the Department of Rivas's ten municipalities in two phases. In phase 1, we screened participants using a field-based capillary creatinine measuring system and collected self-reported information on lifestyle and occupational, exposure, and health histories. Two years later, in phase 2, we enrolled 222 new participants, performing serum creatinine testing in these participants and confirmatory serum creatinine testing in phase 1 participants.

RESULTS

We enrolled 1242 of 1397 adults (89%) living in 533 households (median age 41 years; 43% male). We confirmed CKD (eGFR<60 ml/min per 1.73 m²) in 53 of 1227 (4.3%) evaluable participants. In multivariable testing, risk factors for prevalent CKD included age (odds ratio [OR], 1.92; 95% confidence interval [95% CI], 1.89 to 1.96) and self-reported history of hypertension (OR, 1.95; 95% CI, 1.04 to 3.64), diabetes (OR, 2.88; 95% CI, 1.40 to 5.93), or current or past work in the sugarcane industry (OR 2.92; 95% CI, 1.36 to 6.27).

CONCLUSIONS

Adjusted CKD prevalence was about 5% with repeat confirmatory testing in southwest Nicaragua, lower than in the northwest region. Risk factors included diabetes, hypertension, and current or prior work in the sugarcane industry but not in other forms of agricultural work. Formal CKD surveillance programs in Nicaragua are needed to assess the overall burden of CKD nationally, with a focus on agricultural workers.

Trust, Conflict, and Engagement in Occupational Health: North American Epidemiologists Conduct Occupational Study in Communities Affected by Chronic Kidney Disease of Unknown Origin (CKDu)

PURPOSE OF REVIEW

Science has been used as a tool of colonialism, and aspects of science privilege researchers in the global North (USA and Europe). The environmental justice and worker health movements in the USA and globally have influenced aspects of how occupational and environmental health research is conceived and conducted so that it is more equitable. This review provides a case example of research in the area of chronic kidney disease of unknown origin (CKDu).

RECENT FINDINGS

In the present work, the author describes aspects of community-based participatory research and anti-colonial research that influence a current occupational epidemiology study of CKDu in Mesoamerica among workers in agriculture and non-agricultural industries. The research includes investigators from numerous countries in the global North and South and funding from the US government and corporations. The role of industry in science and the misuse of science by corporate interests remain substantial threats to research integrity. The ability of researchers to navigate potentially conflicting interests with industry and workers, and establish trust within and outside the scientific community, is essential for sustained engagement in longitudinal studies. Trust is about human relationships. It takes time and effort to build and is essential for creating equitable, empowering research relationships.

Serum and urine fluoride levels in populations of high environmental fluoride exposure with endemic CKDu: a case-control study from Sri Lanka

Chronic kidney disease of uncertain etiology (CKDu) is a common health issue among farming communities in the dry zone of Sri Lanka where groundwater fluoride is known to be higher than recommended levels. Excessive environmental ingestion of fluoride is widely considered as a possible factor for the onset of CKDu. This study was carried out to evaluate the serum and urine fluoride levels in biopsy-proven, non-dialysis CKDu patients. Control subjects were selected from the same area without any deteriorated kidney functions. Serum and urine fluoride levels were determined by ion-selective electrode method. Higher content of serum and urine fluoride levels were observed in patients with chronic renal failures. In CKDu cases, the serum fluoride concentrations ranged between 0.47 and 9.58 mg/L (mean 1.39 ± 1.1 mg/L), while urine levels were varied between 0.45 and 6.92 mg/L (mean 1.53 ± 0.8 mg/L). In patients, urine fluoride levels showed a significant difference with the CKDu stage; however, no difference was obtained between genders and age. In endemic controls, serum and urine fluoride levels ranged between 0.51 and 1.92 mg/L (mean = 1.07 ± 0.3 mg/L) and 0.36 and 3.80 mg/L (mean = 1.26 ± 0.6 mg/L), respectively. Significantly higher fluoride in serum and urine was noted in CKDu patients compared to endemic control groups. Higher fluoride exposure via drinking water is possibly the reason for higher fluoride in serum, while excessive urinary excretion would be due to deterioration of the kidney, suggesting a possible nephrotoxic role of environmental fluoride exposure.

Mesoamerican Nephropathy

Mesoamerican endemic nephropathy is a type of chronic kidney disease of unknown origin, present in pockets of high prevalence along the Pacific Ocean coast of the Mesoamerican region, from southwest Mexico to Costa Rica. The disease is common in young adult men, most often yet not exclusively from agricultural communities, and with a high mortality rate. Kidney biopsy specimens show primarily tubular atrophy and interstitial fibrosis with some glomerular changes attributed to ischemia. Exposure to agrochemicals, heavy metals or metalloids, intense physical activity under heat stress with dehydration, infections, among other possible causes have been hypothesized as the culprit of the disease. Hypokalemia and hyperuricemia are frequent clinical features. Early diagnosis is key to initiate timely treatment and slow down the progression to end-stage kidney disease. At present, our knowledge about the magnitude of the disease burden imposed by Mesoamerican endemic nephropathy is clearly incomplete and its cause has not been determined. There is a need to implement epidemiologic and mechanistic research projects as well as formal chronic kidney disease and end-stage kidney disease registries in the Mesoamerican region to better understand the real extent of the epidemic, delimit risk populations, and to construct sound public health policy decisions.

Longitudinal trends in renal function among first time sugarcane harvesters in Guatemala

Introduction

Chronic kidney disease of unknown origin (CKDu) is an epidemic concentrated in agricultural communities in Central and South America, including young, male sugarcane harvesters. The purpose of this analysis is to understand early changes in kidney function among a cohort of first-time sugarcane harvesters and to determine risk factors for kidney function decline.

Methods

Joint latent class mixed models were used to model sub-population kidney function trajectory over the course of 4 years (2012–2016). Probability weighted logistic regression was used to determine personal health, community, and individual behavior risk factors associated with sub-population assignment. Data analysis occurred in 2019.

Results

Of 181 new workers median age 19 years old (IQR: 4), 39 (22%) were identified as having non-stable kidney function with an annual age-adjusted decline of estimated glomerular filtration rate (eGFR) of -1.0 ml/min per 1.73 m² (95% CI: -3.4, 1.3). Kidney function (OR: 0.96; 95% CI: 0.93, 0.98), mild hypertension (OR: 5.21; 95% CI: 2.14, 13.94), and having a local home of residence (OR: 7.12; 95% CI: 2.41, 26.02) prior to employment in sugarcane were associated with non-stable eGFR sub-population assignment.

Conclusions

Mild hypertension may be an early indicator of the development of CKDu. A better understanding of preexisting risk factors is needed to determine why individuals are entering the workforce with reduced kidney function and elevated blood pressure and increased risk of renal function decline.

Investigating Possible Infectious Causes of Chronic Kidney Disease of Unknown Etiology in a Nicaraguan Mining Community

A chronic kidney disease of unknown etiology (CKDu) has been killing workers in Central America. Occupational heat stress is thought to play an important role. Leptospirosis and hantavirus have been suggested as additional possible risk factors. In a case–control study in a Nicaraguan mining community, a structured survey was administered to adults, and biological measurements and specimens were taken. Serum was analyzed for antibodies to Leptospira and hantavirus. Before statistical analysis, a board-certified nephrologist determined final case and control status based on serum creatinine and other laboratory values. Multivariable analysis was by logistic regression. In sensitivity analyses, cases were restricted to those diagnosed with CKDu in the previous 3 years. Of 320 eligible participants, 112 were classified as presumptive cases, 176 as controls and 32 as indeterminant. The risk of CKDu in those ever having worked in mining or construction was 4.4 times higher than in other participants (odds ratio = 4.44, 95% CI: 1.96–10.0, P = 0.0003). Eighty-three (26%) of the 320 participants were seropositive for at least one tested strain of Leptospira. No evidence of a causal link between leptospirosis or hantavirus and CKDu was found. The sensitivity analyses provide some evidence against the hypotheses that leptospirosis or hantavirus leads to CKDu within a few years. A major limitation was the impossibility of determining the absolute or relative timing of infection and CKDu onset. A prospective cohort design, with repeated collection of specimens over several years, could yield clearer answers about infections as potential etiologic agents in CKDu.

Chronic kidney disease of non-traditional origin in Mesoamerica: a disease primarily driven by occupational heat stress

The death toll of the epidemic of chronic kidney disease of nontraditional origin (CKDnt) in Mesoamerica runs into the tens of thousands, affecting mostly young men. There is no consensus on the etiology. Anecdotal evidence from the 1990s pointed to work in sugarcane; pesticides and heat stress were suspected. Subsequent population-based surveys supported an occupational origin with overall high male-female ratios in high-risk lowlands, but small sex differences within occupational categories, and low prevalence in non-workers. CKDnt was reported in sugarcane and other high-intensity agriculture, and in non-agricultural occupations with heavy manual labor in hot environments, but not among subsistence farmers. Recent studies with stronger designs have shown cross-shift changes in kidney function and hydration biomarkers and cross-harvest kidney function declines related to heat and workload. The implementation of a water-rest-shade intervention midharvest in El Salvador appeared to halt declining kidney function among cane cutters. In Nicaragua a water-rest-shade program appeared sufficient to prevent kidney damage among cane workers with low-moderate workload but not among cutters with heaviest workload. Studies on pesticides and infectious risk factors have been largely negative. Non-occupational risk factors do not explain the observed epidemiologic patterns. In conclusion, work is the main driver of the CKDnt epidemic in Mesoamerica, with occupational heat stress being the single uniting factor shown to lead to kidney dysfunction in affected populations. Sugarcane cutters with extreme heat stress could be viewed as a sentinel occupational population. Occupational heat stress prevention is critical, even more so in view of climate change.

Rationale and population-based prospective cohort protocol for the disadvantaged populations at risk of decline in eGFR (CO-DEGREE)

INTRODUCTION

A recently recognised form of chronic kidney disease (CKD) of unknown origin (CKDu) is afflicting communities, mostly in rural areas in several regions of the world. Prevalence studies are being conducted in a number of countries, using a standardised protocol, to estimate the distribution of estimated glomerular filtration rate (eGFR), and thus identify communities with a high prevalence of reduced glomerular filtration rate (GFR). In this paper, we propose a standardised minimum protocol for cohort studies in high-risk communities aimed at investigating the incidence of, and risk factors for, early kidney dysfunction.

METHODS AND ANALYSIS

This generic cohort protocol provides the information to establish a prospective population-based cohort study in low-income settings with a high prevalence of CKDu. This involves a baseline survey that included key elements from the DEGREE survey (eg, using the previously published DEGREE methodology) of a population-representative sample, and subsequent follow-up visits in young adults (without a pre-existing diagnosis of CKD (eGFR<60 mL/min/1.73m2), proteinuria or risk factors for CKD at baseline) over several years. Each visit involves a core questionnaire, and collection and storage of biological samples. Local capacity to measure serum creatinine will be required so that immediate feedback on kidney function can be provided to participants. After completion of follow-up, repeat measures of creatinine should be conducted in a central laboratory, using reference standards traceable to isotope dilution mass spectrometry (IDMS) quality control material to quantify the main outcome of eGFR decline over time, alongside a description of the early evolution of disease and risk factors for eGFR decline.

ETHICS AND DISSEMINATION

Ethical approval will be obtained by local researchers, and participants will provide informed consent before the study commences. Participants will typically receive feedback and advice on their laboratory results, and referral to a local health system where appropriate.

Distribution and Determinants of Chronic Kidney Disease of Unknown Etiology: A Brief Overview

Globally, 33187000 DALYs and 956000 deaths are attributed to chronic kidney disease (CKD) every year. Diabetes and hypertension are the two most common causes of CKD. Another category of CKD without any known common causes, chronic kidney disease of unknown etiology (CKDu) is also increasingly reported from different regions of the world such as Central America, Sri Lanka, and India. They are predominately observed in agricultural communities where crops such as sugarcane and coconut are commonly cultivated. Young adults and males are at higher risk of developing CKDu. It mainly affects individuals belonging to lower socioeconomic status. Exposure to silica, arsenic, and fluoride might be associated with increased prevalence of CKDu. The role of heat stress in contributing to CKD through dehydration is unclear but cannot be ruled out. Mycotoxins such as aflatoxins and ochratoxins are also found to be associated with CKDu in some settings. Several studies have reported that CKDu has a significant positive association with pesticides used in agriculture such as HCH, Endosulfan, Alachlor, and Pendimethalin. There is also a possible role of infections by Hantavirus and Leptospirosis in acute febrile phase of CKDu. However, there is no conclusive evidence from studies conducted on CKDu regarding its causes and risk factors. Therefore, large-scale studies with better methodology need to be conducted to study the etiology and pathogenesis of CKDu in various settings.

The Potential for Renal Injury Elicited by Physical Work in the Heat

An epidemic of chronic kidney disease (CKD) is occurring in laborers who undertake physical work in hot conditions. Rodent data indicate that heat exposure causes kidney injury, and when this injury is regularly repeated it can elicit CKD. Studies in humans demonstrate that a single bout of exercise in the heat increases biomarkers of acute kidney injury (AKI). Elevations in AKI biomarkers in this context likely reflect an increased susceptibility of the kidneys to AKI. Data largely derived from animal models indicate that the mechanism(s) by which exercise in the heat may increase the risk of AKI is multifactorial. For instance, heat-related reductions in renal blood flow may provoke heterogenous intrarenal blood flow. This can promote localized ischemia, hypoxemia and ATP depletion in renal tubular cells, which could be exacerbated by increased sodium reabsorption. Heightened fructokinase pathway activity likely exacerbates ATP depletion occurring secondary to intrarenal fructose production and hyperuricemia. Collectively, these responses can promote inflammation and oxidative stress, thereby increasing the risk of AKI. Equivalent mechanistic evidence in humans is lacking. Such an understanding could inform the development of countermeasures to safeguard the renal health of laborers who regularly engage in physical work in hot environments.

Pilot Study of Renal Urinary Biomarkers for Diagnosis of CKD of Uncertain Etiology

Introduction

Chronic kidney disease of uncertain etiology (CKDu), an emerging chronic kidney disease (CKD) subtype, contributes to significant morbidity and mortality in certain tropical countries. Although several indicators of CKDu have been previously suggested, sensitive and specific tests to detect early disease or predict disease progression are currently unavailable. This study focused on evaluating 8 renal urinary markers, namely neutrophil gelatinase-associated lipocalin (NGAL), Kidney Injury Molecule-1 (KIM1), cystatin C (CST3), beta 2 microglobulin (B2M), osteopontin (OPN), alpha 1 microglobulin (A1M), tissue inhibitor of metalloproteinase 1 (TIMP1), and retinol binding protein 4 (RBP4), with the hypothesis that these have distinct expression patterns in patients with CKDu.

Methods

A cross-sectional study was conducted with 5 study groups comprising subjects from CKDu, endemic CKD, nonendemic CKD, and endemic healthy and nonendemic healthy controls. The urinary levels of the 8 selected renal biomarkers were quantified using multiplex biomarker assay, and the data were subjected to systematic analysis using logistic regression algorithm aiming to extract the best marker combination that could distinctly identify the disease groups noninvasively from the healthy controls.

Results

A 3-marker signature panel comprising A1M, KIM1, and RBP4 was identified to represent the best minimum marker combination for differentiating all CKD categories, including CKDu, from healthy controls with an overall sensitivity of ≥0.867 and specificity ≥0.765. The marker combination comprising OPN, KIM1, and RBP4 showed high predictive performance for distinguishing patients with CKDu from patients with CKD with both sensitivity and specificity ≥0.93, which was superior to any existing noninvasive indicator.

Conclusion

In all, our systematic evaluation of urinary markers previously linked to CKD, in general, allowed identification of exclusive marker panel combination for early diagnosis and confirmation of CKDu.

Prevalence and risk factors for impaired kidney function in the district of Anuradhapura, Sri Lanka: a cross-sectional population-representative survey in those at risk of chronic kidney disease of unknown aetiology

BACKGROUND

Over the last 20 years there have been reports of a form of chronic kidney disease of unknown cause (CKDu) affecting rural communities in the North Central Province of Sri Lanka. Valid prevalence estimates, using a standardised methodology, are needed to assess the burden of disease, assess secular trends, and perform international comparisons.

METHODS

We conducted a cross-sectional representative population survey in five study areas with different expected prevalences of CKDu. We used a proxy definition of CKDu involving a single measure of impaired kidney function (eGFR< 60 mL/min/1.7m², using the CKD-Epi formula) in the absence of hypertension, diabetes or heavy proteinuria.

RESULTS

A total of 4803 participants (88.7%) took part in the study and 202 (6.0%; 95% CI 5.2-6.8) had a low eGFR in the absence of hypertension, diabetes and heavy proteinuria and hence met the criteria for proxy CKDu. The proportion of males (11.2%; 95% CI 9.2-13.1) were triple than the females (3.7%; 95% CI 2.9-4.5). Advancing age and history of CKD among parents or siblings were risk factors for low GFR among both males and females while smoking was found to be a risk factor among males.

CONCLUSIONS

These data, collected using a standardised methodology demonstrate a high prevalence of impaired kidney function, not due to known causes of kidney disease, in the selected study areas of the Anuradhapura district of Sri Lanka. The aetiology of CKDu in Sri Lanka remains unclear and there is a need for longitudinal studies to describe the natural history and to better characterise risk factors for the decline in kidney function.

Prevalence and risk factors for impaired kidney function in the district of Anuradhapura, Sri Lanka: a cross-sectional population-representative survey in those at risk of chronic kidney disease of unknown aetiology

Background

Over the last 20 years there have been reports of a form of chronic kidney disease of unknown cause (CKDu) affecting rural communities in the North Central Province of Sri Lanka. Valid prevalence estimates, using a standardised methodology, are needed to assess the burden of disease, assess secular trends, and perform international comparisons.

Methods

We conducted a cross-sectional representative population survey in five study areas with different expected prevalences of CKDu. We used a proxy definition of CKDu involving a single measure of impaired kidney function (eGFR< 60 mL/min/1.7m², using the CKD-Epi formula) in the absence of hypertension, diabetes or heavy proteinuria.

Results

A total of 4803 participants (88.7%) took part in the study and 202 (6.0%; 95% CI 5.2–6.8) had a low eGFR in the absence of hypertension, diabetes and heavy proteinuria and hence met the criteria for proxy CKDu. The proportion of males (11.2%; 95% CI 9.2–13.1) were triple than the females (3.7%; 95% CI 2.9–4.5). Advancing age and history of CKD among parents or siblings were risk factors for low GFR among both males and females while smoking was found to be a risk factor among males.

Conclusions

These data, collected using a standardised methodology demonstrate a high prevalence of impaired kidney function, not due to known causes of kidney disease, in the selected study areas of the Anuradhapura district of Sri Lanka. The aetiology of CKDu in Sri Lanka remains unclear and there is a need for longitudinal studies to describe the natural history and to better characterise risk factors for the decline in kidney function.

Electronic supplementary material

The online version of this article (10.1186/s12889-019-7117-2) contains supplementary material, which is available to authorized users.

Chronic Kidney Disease Among Workers: A Review of the Literature

For the past two decades, agricultural workers in regions of Central America have reported an epidemic of chronic kidney disease of undetermined etiology (CKDu) that is not associated with established risk factors of chronic kidney disease. Several hypotheses have emerged, but the etiology of CKDu remains elusive and controversial. The aim of this literature review was to describe the potential risk factors of CKDu in Mesoamerica and implications for the U.S. agricultural worker population. PubMed and CINAHL databases were searched for articles published between 2000 and 2018 that examined CKDu in Mesoamerica; 29 original studies were included in this review. CKDu is a multifactorial disease that is often asymptomatic with hallmark characteristics of elevated serum creatinine and blood urea nitrogen (BUN), low glomerular filtration rate, electrolyte abnormalities, and non-nephrotic proteinuria. Reducing the global prevalence of CKDu will require more robust studies on causal mechanisms and on interventions that can reduce morbidity and mortality in vulnerable populations.

Evaluation of emerging biomarkers of renal damage and exposure to aflatoxin-B1 in Mexican indigenous women: a pilot study

Aflatoxins (AFs) are mycotoxins produced by Aspergillus parasiticus and Aspergillus flavus which frequently contaminate maize. These compounds are considered toxic, especially AFB1 which has been classified as a human carcinogen, due to its relationship with the generation of hepatocellular carcinoma. Studies in vivo, in animal models, prove that chronic consumption of AFB1 has an association with renal adverse effects, but evidence in humans is scarce. Therefore, the main objective of this research was to conduct a pilot study to evaluate the correlation between exposure to AFB1 and early-stage renal damage in indigenous women of San Luis Potosí, Mexico. Exposure to AFB1 was measured through the biomarker AFB1-lysine and renal damage through kidney injury molecule-1 (KIM-1), neutrophil gelatinase-associated lipocalin (NGAL), and cystatin-C (Cys-C). AFB1-Lys was measured by HPLC-FLD. The method was validated with a correlation coefficient of 0.99 and limit of detection and quantification of 3.5 and 4.7 pg mL-1, respectively. Levels of NGAL, KIM-1, and Cys-C were determined (median (P25-P75), 5.96 (3.16-15.91), 0.137 (0.137-0.281), and 18.49 (5.76-29.57) ng mL-1, respectively). Additionally, glomerular filtration rate (GFR) (83.3 (59.8-107.4) mL/min/1.73 m2) and serum creatinine (SCr) (0.88 (0.72-1.22) mg dL-1) were obtained. The median concentrations for AFB1-Lys were 2.08 (1.89-5.8) pg mg-1 of albumin. Statistically significant correlations between AFB1-Lys/KIM-1 (Rho = 0.498, p = 0.007) and AFB1/Cys-C (Rho = 0.431, p = 0.014) were found. Our results indicate that women are exposed to AFB1, due to the fact that the AFB1-Lys biomarker was found in a high percentage of the study population (83%). In addition, the results of exposure to AFB1 show a strong significant correlation between KIM-1 and Cys-C that may indicate the toxic renal effect. These results are alarming because of the high toxicity of this compound and require adequate intervention to reduce AFB1 exposure in these populations.

Risk factors for chronic kidney disease of non-traditional causes: a systematic review

OBJECTIVES

To evaluate the potential associations between chronic kidney disease of uncertain or non-traditional etiology (CKDnT) and agrochemicals, heat stress, heavy metals, and other factors identified in the literature in any region of the world and at any time.

METHODS

This was a systematic review of the most frequent exposures suspected to be possible causes of CKDnT. A search was conducted of PubMed, LILACS, World Wide Science electronic databases, among other sources. Only medium- and high-quality studies were included. The synthesis of evidence included a narrative synthesis, meta-analysis, and meta-regression.

RESULTS

Four systematic reviews and 61 primary studies were included. Results of the meta-analysis suggest that exposure to agrochemicals and working in agriculture increase the risk of CKDnT, but this only reached significance for working in agriculture. When cross-sectional studies were excluded, agrochemical exposure became significant. However, there is substantial heterogeneity in the effect sizes.

CONCLUSIONS

Based on the existing evidence and the precautionary principle, it is important to implement preventive measures to mitigate the damage caused by CKDnT to both agricultural workers and their communities (i.e., improvement of working conditions, cautious management of agrochemicals, etc.). More high-quality research is needed to measure impact and to build the evidence base.

Prevalence of and risk factors for chronic kidney disease of unknown aetiology in India: secondary data analysis of three population-based cross-sectional studies

OBJECTIVES

To assess whether chronic kidney disease of unknown aetiology (CKDu) is present in India and to identify risk factors for it using population-based data and standardised methods.

DESIGN

Secondary data analysis of three population-based cross-sectional studies conducted between 2010 and 2014.

SETTING

Urban and rural areas of Northern India (states of Delhi and Haryana) and Southern India (states of Tamil Nadu and Andhra Pradesh).

PARTICIPANTS

12 500 individuals without diabetes, hypertension or heavy proteinuria.

OUTCOME MEASURES

Mean estimated glomerular filtration rate (eGFR) and prevalence of eGFR below 60 mL/min per 1.73 m2 (eGFR <60) in individuals without diabetes, hypertension or heavy proteinuria (proxy definition of CKDu).

RESULTS

The mean eGFR was 105.0±17.8 mL/min per 1.73 m2. The prevalence of eGFR <60 was 1.6% (95% CI=1.4 to 1.7), but this figure varied markedly between areas, being highest in rural areas of Southern Indian (4.8% (3.8 to 5.8)). In Northern India, older age was the only risk factor associated with lower mean eGFR and eGFR <60 (regression coefficient (95% CI)=-0.94 (0.97 to 0.91); OR (95% CI)=1.10 (1.08 to 1.11)). In Southern India, risk factors for lower mean eGFR and eGFR <60, respectively, were residence in a rural area (-7.78 (-8.69 to -6.86); 4.95 (2.61 to 9.39)), older age (-0.90 (-0.93 to -0.86); 1.06 (1.04 to 1.08)) and less education (-0.94 (-1.32 to -0.56); 0.67 (0.50 to 0.90) for each 5 years at school).

CONCLUSIONS

CKDu is present in India and is not confined to Central America and Sri Lanka. Identified risk factors are consistent with risk factors previously reported for CKDu in Central America and Sri Lanka.

High Prevalence of CKD of Unknown Etiology in Uddanam, India

INTRODUCTION

There were concerns raised regarding a high prevalence of chronic kidney disease (CKD) in Uddanam, a fertile subtropical low-altitude territory in the southern Indian state of Andhra Pradesh. The present study was undertaken to ascertain the prevalence of CKD, disease characteristics, and risk factor profile in this area.

METHODS

We selected 2210 subjects (age >18 years) using multistage sampling. After obtaining demographic and anthropometric data, urinary protein-creatinine ratio, serum creatinine, and blood glucose were measured in all the subjects. Glomerular filtration rate was estimated (eGFR) using the Modification of Diet in Renal Disease equation.

RESULTS

Mean age of the subjects was 43.2 ± 14.2 years (range: 18-98), 44.3% were men and 55.7% were women. Mean eGFR of subjects was 94.3 ± 33.4. Low eGFR (<60 ml/min per 1.73 m2) was seen in 307 (13.98%) patients with a mean eGFR of 34.8 ± 16.6. The prevalence of subjects having low eGFR and with proteinuria (CKD) was 18.23%. Major risk factors, such as diabetes, long-standing hypertension, and significant proteinuria, were absent in 73% of patients with CKD, implying that a significant proportion of the population is afflicted with the entity "CKD of unknown etiology (CKDu)."

CONCLUSION

The prevalence of CKD and CKDu in Uddanam is much higher than other earlier studies in either rural or urban communities in India. We suggest that there is a dire need to review health policies and allocate resources for prevention and treatment of CKD in the Uddanam region.

Prevalence and Risk Factors for CKD Among Brickmaking Workers in La Paz Centro, Nicaragua

RATIONALE & OBJECTIVE

In Central America, there is a high prevalence of chronic kidney disease (CKD) of nontraditional etiology often observed among agricultural workers. Few studies have assessed CKD prevalence among workers in nonagricultural occupations, which was the objective of this investigation.

STUDY DESIGN

Prospective cohort study.

SETTING & PARTICIPANTS

Male and female workers (n = 224) employed by artisanal brickmaking facilities in La Paz Centro, Nicaragua.

PREDICTORS

Age, sex, education, smoking status, body mass index, alcohol consumption, water consumption, first-degree relative(s) with CKD, years worked, hours worked per week, job category, study visit (baseline and follow-up), and self-reported hypertension and diabetes.

OUTCOMES

CKD defined as estimated glomerular filtration rate (eGFR) < 60mL/min/1.73m² at 2 time points 4 months apart and CKD stage.

ANALYTICAL APPROACH

A linear mixed-effects model with an unstructured covariance matrix was used to evaluate the association between demographics, occupational risk factors, and eGFR at baseline. The interaction between risk factors and time with change in eGFR was also evaluated. Multivariable logistic regression models were used to evaluate predictors of CKD.

RESULTS

The CKD prevalence was 12.1% (n = 27), 100% of cases were male, 30% had stage 5 CKD (eGFR < 15mL/min/1.73m²), and 22% were younger than 35 years. Proportions of participants with eGFRs < 60mL/min/1.73m² at baseline and follow-up were 13.8% and 15.2%, respectively. Linear regression analysis demonstrated significant predictors of lower kidney function at baseline including oven work, older age, lack of education, and having an immediate family member with CKD. Predictors of CKD identified using logistic regression analysis included oven work and lack of education.

LIMITATIONS

Crude job classification measures, loss to follow-up, self-reported exposures.

CONCLUSIONS

The prevalence of CKD is high in this population of brick workers, suggesting that the epidemic of CKD affecting Mesoamerica is not limited to agricultural workers. These results are consistent with the hypothesis that occupational heat exposure is a risk factor for kidney disease in this region.

Prospective Biopsy-Based Study of CKD of Unknown Etiology in Sri Lanka

BACKGROUND AND OBJECTIVES

A kidney disease of unknown cause is common in Sri Lanka's lowland (dry) region. Detailed clinical characterizations of patients with biopsy-proven disease are limited, and there is no current consensus on criteria for a noninvasive diagnosis.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We designed a prospective study in a major Sri Lankan hospital servicing endemic areas to ascertain pathologic and clinical characteristics of and assess risk factors for primary tubulointerstitial kidney disease. We used logistic regression to determine whether common clinical characteristics could be used to predict the presence of primary tubulointerstitial kidney disease on kidney biopsy.

RESULTS

From 600 new patients presenting to a tertiary nephrology clinic over the course of 1 year, 87 underwent kidney biopsy, and 43 (49%) had a biopsy diagnosis of primary tubulointerstitial kidney disease. On detailed biopsy review, 13 (30%) had evidence of moderate to severe active kidney disease, and six (15%) had evidence of moderate to severe chronic tubulointerstitial kidney disease. Patients with tubulointerstitial kidney disease were exclusively born in endemic provinces; 91% spent a majority of their lifespan there. They were more likely men and farmers (risk ratio, 2.0; 95% confidence interval, 1.2 to 2.9), and they were more likely to have used tobacco (risk ratio, 1.7; 95% confidence interval, 1.0 to 2.3) and well water (risk ratio, 1.5; 95% confidence interval, 1.1 to 2.0). Three clinical characteristics-age, urine dipstick for protein, and serum albumin-could predict likelihood of tubulointerstitial kidney disease on biopsy (model sensitivity of 79% and specificity of 84%). Patients referred for kidney biopsy despite comorbid diabetes or hypertension did not experience lower odds of tubulointerstitial kidney disease.

CONCLUSIONS

A primary tubulointerstitial kidney disease occurs commonly in specific regions of Sri Lanka with characteristic environmental and lifestyle exposures.

Identification of young adults at risk of an accelerated loss of kidney function in an area affected by Mesoamerican nephropathy

BACKGROUND

After two-years of follow-up of 263 apparently healthy 18- to 30-year-old men in communities affected by Mesoamerican nephropathy (MeN), we identified three distinct case groups: a subgroup with (i) established renal dysfunction (case-group 1); individuals with (ii) a rapid decline in kidney function (case-group 2); and individuals with (iii) stable kidney function (non-cases). This paper investigates whether local tests are potentially useful for the timely identification of these case groups.

METHODS

Creatinine levels were measured in local laboratories every six months for two years. Aliquots were sent to a centralized laboratory for measurements of cystatin C and creatinine levels. We investigated agreement between the locally and centrally measured creatinine-based Chronic Kidney disease Epidemiology Collaboration (CKD-EPI) equation for estimating the Glomerular Filtration Rate (eGFR). A logistic regression analysis was used to assess predictive factors for case groups 1 and 2 compared to non-cases. Predictive variables were locally measured eGFR, and urinary neutrophil gelatinase-associated lipocalin (uNGAL) levels. The discrimination performance of the model was assessed using the area under the receiver operating characteristic curve (AUC).

RESULTS

Considerable variation in local eGFR measurements was observed. The prediction model for case-group 1 included baseline kidney function and with or without uNGAL (AUC = 0.98, 95% confidence interval (CI), 0.91-1.00). The prediction model for case-group 2 also required eGFRScr at six and twelve months after baseline, with or without uNGAL levels (AUC = 0.88; 95% CI 0.80-0.99).

CONCLUSIONS

Established renal dysfunction was detected at a single time point using local measurements and uNGAL. For the detection of a rapid decline in kidney function over time, at least 2 more measurements at six and twelve months are needed.

Acute Kidney Injury in Sugarcane Workers at Risk for Mesoamerican Nephropathy

RATIONALE & OBJECTIVE

Mesoamerican nephropathy (MeN), a form of chronic kidney disease (CKD) of unknown cause in Central America, affects young individuals working in physically strenuous occupations. Repeated episodes of work-related kidney injury may lead to CKD in this setting. We aimed to better understand the burden and natural history of acute kidney injury (AKI) in workers at risk for MeN.

STUDY DESIGN

Cross-sectional study of active sugarcane workers, followed by prospective follow-up of individuals with AKI.

SETTING & PARTICIPANTS

326 sugarcane workers with normal preharvest serum creatinine (Scr) values and no history of CKD in an MeN hotspot in Nicaragua near the end of the harvest, and prospective follow-up of workers with AKI.

PREDICTOR

AKI during the harvest, as defined by Scr level increase ≥ 0.3mg/dL over baseline to a level ≥ 1.3mg/dL.

OUTCOMES

Kidney function trajectory and development of CKD over 12 months.

ANALYTICAL APPROACH

Linear regression models were used to analyze the association between job category and kidney function. For workers with AKI, the effect of time on Scr level was evaluated using linear mixed effects.

RESULTS

34 of 326 participants were found to have AKI, with a median late-harvest Scr level of 1.64mg/dL in the AKI group. Workers without AKI had a median Scr level of 0.88mg/dL. AKI was more common among cane cutters compared with other field workers. Participants with AKI had variable degrees of kidney function recovery, with median 6- and 12-month Scr values of 1.25 and 1.27mg/dL, respectively (P < 0.001 for each follow-up value compared to late-harvest Scr). When we compared workers' kidney function before the AKI episode to their kidney function at last follow-up, 10 participants with AKI developed de novo estimated glomerular filtration rate < 60mL/min/1.73m² and 11 had a >30% decrease in estimated glomerular filtration rate.

LIMITATIONS

Follow-up limited to 1 year and some loss to follow-up in the prospective component of the study. Broad definition of AKI that includes both acute and subacute kidney injury.

CONCLUSIONS

In a group of sugarcane workers with normal preharvest kidney function, newly decreased kidney function developing during the harvest season was common. Of those with kidney injury, nearly half had established CKD 12 months later.

Unadjusted point of care creatinine results overestimate acute kidney injury incidence during field testing in Guatemala

OBJECTIVE

Acute kidney injury (AKI) occurs at high rates among agricultural workers (12-33%) in tropical environments. Because of the remote locations affected, traditional laboratory services are often unavailable. In this study we compare point of care (POC) creatinine values to standardized laboratory values, and examine the effect of POC testing on the interpretation of AKI rates under tropical field conditions.

METHODS

Blood samples were collected from 104 sugarcane workers from two time points in January 2018 as a derivation cohort, and from 105 workers from February to April 2017 as a validation cohort. Finger stick and venipuncture samples were drawn at the end of a worker's shift to measure creatinine. Laboratory samples were tested in Guatemala City, Guatemala, in duplicate using the Jaffe Generation 2 method. An adjustment factor to improve agreement with serum creatinine was statistically derived and validated, and then used to determine impact on observed rates of acute kidney injury based on across shift changes in creatinine.

RESULTS

POC creatinine and serum creatinine measures showed that POC consistently overestimated the creatinine by an average of 22% (95% CI: 19.8%, 24.7%) and the disagreement appeared greater at higher values of serum creatinine. An adjustment factor of 0.7775 was applied, which led to significantly greater agreement between the two measures. Rates of AKI in the two combined groups fell from 72% before adjustment to 57% afterwards.

CONCLUSIONS

POC testing under tropical field conditions routinely overestimates creatinine compared to laboratory testing, which leads to overestimation of rates of acute kidney injury. The application of an adjustment factor significantly improved the accuracy of the POC value.

Kidney progression project (KiPP): Protocol for a longitudinal cohort study of progression in chronic kidney disease of unknown etiology in Sri Lanka

Over the last two decades, a global epidemic of chronic kidney disease of unknown etiology (CKDu) has emerged in rural, arid, agricultural, lowland areas. Endemic regions have reported 15 to 20% prevalence among residents aged 30-60 years. CKDu is a progressive and irreversible disease resulting in renal failure and death in the absence of dialysis or a kidney transplant. While much of the research has focused on identifying etiology, this project seeks to ascertain factors associated with the rapidity of kidney disease progression in one of Sri Lanka's CKDu endemic areas. A sample of 296 male and female residents aged 21 to 65 with moderate CKD, as measured by their serum creatinine level, and a clinical diagnosis of CKDu are followed using quarterly serum testing to track the rate of progression. A baseline survey administered to the entire sample addresses potential risk factors, supplemented by a short survey focusing on changes through time. Concurrently water, soil and air are tested at the local and household levels. The study is the first to foster a multi-disciplinary approach that focuses on disease progression, identifying behavioural and exposure risk factors for rapid kidney function decline, in this progressively fatal disease.

Decline in Kidney Function among Apparently Healthy Young Adults at Risk of Mesoamerican Nephropathy

Background Epidemic levels of CKD of undetermined cause, termed Mesoamerican nephropathy in Central America, have been found in low- and middle-income countries. We investigated the natural history of, and factors associated with, loss of kidney function in a population at high risk for this disease.Methods We conducted a 2-year prospective, longitudinal study with follow-up every 6 months in nine rural communities in northwestern Nicaragua and included all men (n=263) and a random sample of women (n=87) ages 18-30 years old without self-reported CKD, diabetes, or hypertension. We used growth mixture modeling to identify subgroups of eGFR trajectory and weighted multinomial logistic regression to examine associations with proposed risk factors.Results Among men, we identified three subpopulations of eGFR trajectory (mean baseline eGFR; mean eGFR change over follow-up): 81% remained stable (116 ml/min per 1.73 m2; -0.6 ml/min per 1.73 m2 per year), 9.5% experienced rapid decline despite normal baseline function (112 ml/min per 1.73 m2; -18.2 ml/min per 1.73 m2 per year), and 9.5% had baseline dysfunction (58 ml/min per 1.73 m2; -3.8 ml/min per 1.73 m2 per year). Among women: 96.6% remained stable (121 ml/min per 1.73 m2; -0.6 ml/min per 1.73 m2 per year), and 3.4% experienced rapid decline (132 ml/min per 1.73 m2; -14.6 ml/min per 1.73 m2 per year; n=3 women). Among men, outdoor and agricultural work and lack of shade availability during work breaks, reported at baseline, were associated with rapid decline.Conclusions Although Mesoamerican nephropathy is associated with agricultural work, other factors may also contribute to this disease.

What do epidemiological studies tell us about chronic kidney disease of undetermined cause in Meso-America? A systematic review and meta-analysis

BACKGROUND

The aim of this systematic review is to examine the epidemiological knowledge and gaps in understanding of the potential causes of chronic kidney disease of undetermined cause (CKDu) in Meso-America.

METHODS

A systematic literature search of epidemiological studies of CKDu was conducted in PubMed, Embase and Web of Science from January 2000 to January 2017. Study quality was assessed by adapting the tool from Higgins et al. for observational studies. Where applicable, the summary prevalence odds ratio (POR) and 95% confidence interval (CI) were calculated using a random effects model.

RESULTS

Twenty-five epidemiological studies were included in the analysis of risk factors for CKDu. The quality assessment of each occupational and community study was medium. The PORs for CKDu were males versus females 2.42 (95% CI 1.76-3.08), family history of CKD (versus none) 1.84 (95% CI 1.37-2.30), high water intake (versus low) 1.61 (95% CI 1.01-2.21) and low altitude (versus highland) 2.09 (95% CI 1.00-3.17). There were no significant associations between CKDu and pesticide exposure (versus no) 1.17 (95% CI 0.87-1.46), alcohol consumption (versus no) 1.34 (95% CI 0.84-1.84), non-steroidal anti-inflammatory drugs (versus no) 0.99 (95% CI 0.60-1.39) and heat stress (versus no) 1.52 (95% CI -0.91 - 3.95).

CONCLUSION

Our meta-analysis showed positive associations for males (versus females) and family history of CKD, water intake, lowland altitude and CKDu. There were no significant associations with pesticide exposure, non-steroidal anti-inflammatory drugs intake, heat stress and alcohol consumption.

Chronic Kidney Disease, Gender, and Access to Care: A Global Perspective

Little is known regarding the ways in which chronic kidney disease (CKD) prevalence and progression differ between the sexes. Still less is known regarding how social disparities between men and women may affect access to care for CKD. In this review, we briefly describe biological sex differences, noting how these differences currently do not influence CKD management recommendations. We then describe what is known within the published literature regarding differences in CKD epidemiology between sexes; namely prevalence, progression, and access to treatment throughout the major world regions. We highlight that health care expenditure and social gender disparities ultimately may determine whether women have equitable access to care for CKD and end-stage kidney disease. Among many high- and low-income settings, women more often donate and are less likely to receive kidney transplants when compared with men. Research is needed urgently to elucidate the reasons behind these disparities, as well as to develop CKD treatment strategies tailored to women's unique health care needs.

Recent trends in the prevalence of chronic kidney disease: not the same old song

PURPOSE OF REVIEW

We aim to review recent updates on the epidemiology of chronic kidney disease (CKD).

RECENT FINDINGS

Recent analyses from the National Health and Nutritional Examination survey describe the temporal trend in CKD prevalence in US adults. The overall prevalence of estimated glomerular filtration rate less than 60 ml/min/1.73 m increased from 4.8% in 1988-1994 to 6.9% in 2003-2004, but has since stabilized at 6.4-6.9% up to 2011-2012. Prevalence of CKD stages 1-4 has also stabilized at ∼14% of adults since 2003-2004. The prevalence of diabetic kidney disease - defined as estimated glomerular filtration rate less than 60 ml/min/1.73 m and/or microalbuminuria among adults with diabetes - has similarly plateaued since the early to mid-2000s at ∼26-27%. There is continued rise in CKD and diabetic kidney disease prevalence among blacks and Mexican-Americans, however, in the last decade. Worldwide, a similar pattern of stable prevalence of CKD since the early 2000s is seen in England, Norway, and Korea. Despite these optimistic findings, there are several emerging at-risk populations. Rapid increases in diabetes and hypertension in China may signal an impending growth in CKD. In parts of Central America, there is emergence of very high CKD prevalence among agricultural workers - suspected to be due to occupational and environmental exposures.

SUMMARY

Collective efforts to undermine risk factors, such as better control of hypertension and diabetes, have likely helped to abate the growth in CKD in several developed countries within the last decade. More worldwide high-quality and geographically granular data collection on CKD would help to monitor the epidemiology of CKD and potentially assist in identifying impactful interventions.

[Establishing research priorities for chronic kidney disease of non-traditional causes in Central AmericaDeterminação de prioridades em pesquisa da doença renal crônica associada a causas não tradicionais na América Central]

Introducción

En 2013, los Estados Miembros de la OPS reconocieron la epidemia de enfermedad renal crónica de causas no tradicionales (ERCnT) como un grave problema de salud pública. Este artículo describe el establecimiento de prioridades de investigación para abordar de manera integral la ERCnT en Centroamérica.

Métodos

Se estructuró una encuesta virtual utilizando la metodología Delphi mediante una búsqueda de estudios de investigación efectuados en Centroamérica y de agendas de investigación previas sobre la ERC. Los encuestados se identificaron en diversas fuentes. La primera ronda buscó refinar y añadir tópicos de investigación y priorizar los más relevantes. La segunda ronda priorizó los tópicos más relevantes. Se realizó un análisis por fuzzy sets para estimar umbrales de decisión y puntajes por tópico.

Resultados

La encuesta se envió a 83 personas de habla hispana y 38 de habla inglesa y respondió 46,2%. Para la segunda ronda, se envió la encuesta a 56 personas en español y 16 en inglés que habían contestado a la la primera. Se priorizaron 18 tópicos de investigación enmarcados en 10 áreas: políticas públicas, determinantes, etiología, diagnóstico y tratamiento de la ERC, prevención primaria, prestación de servicios, recursos humanos, sistemas de información y financiamiento. Se comprobó que la investigación en ERCnT es escasa y está restringida a ciertos tópicos.

Conclusiones

Además de los factores etiológicos, se dio gran relevancia a aspectos relacionados con la respuesta de los sistemas de salud, incluidos el abordaje de la prestación de servicios, los recursos humanos, el financiamiento y aspectos ocupacionales y ambientales.

Chronic kidney disease mortality trends in selected Central America countries, 1997-2013: clues to an epidemic of chronic interstitial nephritis of agricultural communities

BACKGROUND

In Central America, chronic interstitial nephritis of agricultural communities (CINAC) has reached epidemic proportions. Clusters of cases have been described in several farming communities. Its aetiology remains uncertain and a controversy exists on its key triggers, among them the heat stress-dehydration mechanism and the toxic exposure to agrochemicals.

METHODS

This study analysed the mortality pattern and trend of chronic kidney disease code N18 (CKD-N18) according to the International Statistical Classification of Diseases and Related Health Problems-10th Revision, the proxy and the underlying cause of death, in four selected Central American countries from 1997 to 2013. In addition, we used exponential regression to retrospectively model the likely onset and prior trajectory of the epidemic.

RESULTS

Between 1997 and 2013, CKD-N18 mortality accounting 47 885 deaths (31% were female), 19 533 of which occurred below 60 years of age (26% female). The excess of mortality starts as early as 10-14 years of age for both boys and girls. El Salvador and Nicaragua, with mortality rates between 9-fold and 12-fold higher than reference countries, were the most affected. Statistical modelling suggests that the epidemic commenced around the mid-1970s, coinciding with important changes in modes of agricultural production.

CONCLUSIONS

This study provides the most comprehensive mortality analysis of this epidemic published to date and confirms an excess of CKD-N18 mortality and its relation with the epidemic of CINAC. The overall trends and the mortality pattern among women, children and adolescents suggest that the heat stress-dehydration hypothesis cannot fully explain this epidemic and that other environmental factors, more likely agricultural practices and agrochemicals, may be causally involved.

Chronic kidney disease in sugarcane workers in Cameroon: a cross-sectional study

BACKGROUND

Agricultural workers especially in sugarcane plantations have a high risk of chronic kidney disease (CKD). Little is known about CKD among sugarcane plantation workers in Cameroon. This study sought to evaluate the prevalence and identify factors associated with CKD in sugarcane plantation workers in Cameroon.

METHODS

We conducted an analytic cross-sectional study including 204 adult workers at the sugarcane plantation complex in Mbandjock, Cameroon; over 500 m above sea level. Chronic kidney disease (proteinuria as estimated by urine dipstick analysis and/or estimated glomerular filtration rate < 60 ml/min/1.73 m2 persistent after 3 months) was the outcome of interest. Those with abnormal results were seen again after 3 months to confirm the diagnosis. We evaluated the association between CKD and participant age, sex, contract-type, duration of employment, socio-economic status, workspace, exposure to agrochemicals, heavy metals and heat, selected risk factors and co-morbid conditions.

RESULTS

The overall prevalence of CKD was 3.4%. The factory workers were the most affected (7%), compared to the field (2.4%) and office workers (0%). 2.9% of the participants had persistent proteinuria, mild in every case, and 0.5% of them had an estimated glomerular filtration rate < 60 ml/min/1.73 m2. Age ≥ 40 years was an independent predictor of CKD.

CONCLUSION

The prevalence of CKD among employees of the Mbandjock sugarcane plantation is low, probably reflecting the preventive measures against heat stress and dehydration in place.

Tracing environmental aetiological factors of chronic kidney diseases in the dry zone of Sri Lanka-A hydrogeochemical and isotope approach

Chronic kidney disease of unknown aetiologies (CKDu) is increasingly recognized in tropical regions and is now considered a global health problem. A detailed hydrogeochemical investigation has been performed in three CKDu hotspots in Sri Lanka to assess the geo-environmental aetiological factors influencing this disease. A total of 71 ground- and 26 surface water samples were collected from Girandurukotte, Wilgamuwa and Nikawewa regions and analysed for major constituents and trace elements. The affected regions are dominated by Ca-Mg-HCO₃ facies groundwater that is mainly controlled by silicate weathering. Higher levels of fluoride associated with higher hardness is the main feature of groundwater from CKDu regions compared to non-CKDu regions. Results showed that 65% of the wells in the affected regions exceeded the fluoride concentration of 0.5mg/L. Environmental isotopes of groundwater in the CKDu regions are represented by the regression line of δ²H=5.42δ¹⁸O-3.59 (r²=0.916) with a clear isotopic differentiation between local precipitation and groundwater. None of the trace elements exceeded the recommended scales and in most cases levels are negligible in both surface and groundwater in study areas. Therefore, the involvement of trace elements such as Cd, As and Pb can be ignored as causative factors for CKDu. This study highlights the synergistic influence of fluoride and hardness that could enhance the disease, and thereby refute earlier theories that attribute trace elements as causative factors for CKDu. Higher hardness in drinking water also restricts sufficient water uptake, particularly by farmers and which affects the physiological, biochemical and nutritional requirements.

Kidney Diseases in Agricultural Communities: A Case Against Heat-Stress Nephropathy

The beginning of the 21st century has seen the emergence of a new chronic tubulo-interstitial kidney disease of uncertain cause among agricultural communities in Central America and Sri Lanka. Despite many similarities in demography, presentation, clinical features, and renal histopathology in affected individuals in these regions, a toxic etiology has been considered mainly in Sri Lanka, whereas the predominant hypothesis in Central America has been that recurrent acute kidney injury (AKI) caused by heat stress leads to chronic kidney disease (CKD). This is termed the heat stress/dehydration hypothesis. This review attempts to demonstrate that there is sparse evidence for the occurrence of significant AKI among manual workers who are at high risk, and that there is little substantial evidence that an elevation of serum creatinine < 0.3 mg/dl in previously healthy people will lead to CKD even with recurrent episodes. It is also proposed that the extent of global warming over the last half-century was not sufficient to have caused a drastic change in the effects of heat stress on renal function in manual workers. Comparable chronic tubulo-interstitial kidney disease is not seen in workers exposed to heat in most tropical regions, although the disease is seen in individuals not exposed to heat stress in the affected regions. The proposed pathogenic mechanisms of heat stress causing CKD have not yet been proved in humans or demonstrated in workers at risk. It is believed that claims of a global warming nephropathy in relation to this disease may be premature and without convincing evidence.

Do attributes of persons with chronic kidney disease differ in low-income and middle-income countries compared with high-income countries? Evidence from population-based data in six countries

Kidney biopsies to elucidate the cause of chronic kidney disease (CKD) are performed in a minority of persons with CKD living in high-income countries, since associated conditions—that is, diabetes mellitus, vascular disease or obesity with pre-diabetes, prehypertension or dyslipidaemia—can inform management targeted at slowing CKD progression in a majority. However, attributes of CKD may differ substantially among persons living in low-income and middle-income countries (LMICs). We used data from population or community-based studies from five LMICs (China, urban India, Moldova, Nepal and Nigeria) to determine what proportion of persons with CKD living in diverse regions fit one of the three major clinical profiles, with data from the US National Health Nutrition and Examination Survey as reference. In the USA, urban India and Moldova, 79.0%–83.9%; in China and Nepal, 62.4%–66.7% and in Nigeria, 51.6% persons with CKD fit one of three established risk profiles. Diabetes was most common in urban India and vascular disease in Moldova (50.7% and 33.2% of persons with CKD in urban India and Moldova, respectively). In Nigeria, 17.8% of persons with CKD without established risk factors had albuminuria ≥300 mg/g, the highest proportion in any country. While the majority of persons with CKD in LMICs fit into one of three established risk profiles, the proportion of persons who have CKD without established risk factors is higher than in the USA. These findings can inform tailored CKD detection and management systems and highlight the importance of studying potential causes and outcomes of CKD without established risk factors in LMICs.

Clinical Evidence of Acute Mesoamerican Nephropathy

Mesoamerican nephropathy (MeN), an epidemic of unexplained kidney disease in Central America, affects mostly young, healthy individuals. Its etiology is a mystery that requires urgent investigation. Largely described as a chronic kidney disease (CKD), no acute clinical scenario has been characterized. An understanding of the early disease process could elucidate an etiology and guide treatment and prevention efforts. We sought to document the earliest clinical signs in patients with suspected MeN in a high-risk population in Nicaragua. Physicians at a local hospital identified suspect cases and documented clinical/laboratory data, demographics, and medical histories. Over a 1-year period, physicians identified 255 mostly young (median 29 years), male (89.5%) patients with elevated creatinine or reduced creatinine clearance. Mean serum creatinine (2.0 ± 0.6 mg/dL) revealed a 2-fold increase from baseline, and half had stage 2 or 3 acute kidney injury. Leukocyturia (98.4%), leukocytosis (81.4%), and neutrophilia (86.2%) predominated. Nausea (59.4%), back pain (57.9%), fever (54.6%), vomiting (50.4%), headache (47.3%), and muscle weakness (45.0%) were common. A typical case of acute MeN presented with elevated (or increased ≥ 0.3 mg/dL or ≥ 1.5-fold from baseline) creatinine, no hypertension or diabetes, leukocyturia, and at least two of fever, nausea or vomiting, back pain, muscle weakness, headache, or leukocytosis and/or neutrophilia. Rapid progression (median 90 days) to CKD was recorded in 8.5% of patients. This evidence can serve as the basis of a sensitive and urgently needed case definition for disease surveillance of early-stage, acute MeN.

Genetic and environmental risk factors for chronic kidney disease

In order to change the current state of chronic kidney disease knowledge and therapeutics, a fundamental improvement in the understanding of genetic and environmental causes of chronic kidney disease is essential. This article first provides an overview of the existing knowledge gaps in our understanding of the genetic and environmental causes of chronic kidney disease, as well as their interactions. The second part of the article formulates goals that should be achieved in order to close these gaps, along with suggested timelines and stakeholders that are to be involved. A better understanding of genetic and environmental factors and their interactions that influence kidney function in healthy and diseased conditions can provide novel insights into renal physiology and pathophysiology and result in the identification of novel therapeutic or preventive targets to tackle the global public health care problem of chronic kidney disease.

Screening for chronic kidney disease of uncertain aetiology in Sri Lanka: usability of surrogate biomarkers over dipstick proteinuria

Background

The use of dipstick proteinuria to screen Chronic Kidney Disease of uncertain aetiology (CKDu) in Sri Lanka is a recently debated matter of dispute. The aim of this study was to assess the suitability of biomarkers: serum creatinine, cystatin C and urine albumin to creatinine ratio (ACR) for screening CKDu in Sri Lanka.

Methods

Forty-four male CKDu patients and 49 healthy males from a CKDu-endemic region were selected. Meanwhile, 25 healthy males from a non-endemic region were selected as an absolute control. The diagnostic accuracy of each marker was compared using the above three study groups.

Results

In receiver operating characteristics (ROC) plots for creatinine, cystatin C and ACR, values of area under the curve (AUC) were 0.926, 0.920 and 0.737 respectively when CKDu was compared to non-endemic control. When CKDu was compared to endemic control, AUCs of above three analytes were distinctly lower as 0.718, 0.808 and 0.678 respectively. Cystatin C exhibited the highest sensitivity for CKDu when analyzed against both control groups where respective sensitivities were 0.75 against endemic control and 0.89 against non-endemic control. ROC-optimal cutoff limits of creatinine, cystatin C and ACR in CKDu vs non-endemic control were 89.0 μmol/L, 1.01 mg/L and 6.06 mg/g-Cr respectively, whereas in CKDu vs endemic control the respective values were 111.5 μmol/L, 1.22 mg/L and 12.66 mg/g-Cr.

Conclusions

Amongst the three biomarkers evaluated in this study, our data suggest that Cystatin C is the most accurate functional marker in detecting CKDu in endemic regions, yet the high cost hinders its usability on general population. Creatinine is favorable over dipstick proteinuria owing to its apparent accuracy and cost efficiency, while having the ability to complement the kidney damage marker (ACR) in screening. ACR may not be favorable as a standalone screening marker in place of dipstick proteinuria due to its significant decline in sensitivity against the CKDu-endemic population. However, creatinine and ACR in a complementary manner could overcome current shortcomings of dipstick proteinuria and such a dual marker tool could be commodious in screening CKDu-type tubulointerstital diseases. Furthermore, use of ACR may also increase the ability to clinically discriminate CKDu from other glomerular nephropathies.

Pesticide exposures and chronic kidney disease of unknown etiology: an epidemiologic review

The main causes of chronic kidney disease (CKD) globally are diabetes and hypertension but epidemics of chronic kidney disease of unknown etiology (CKDu) occur in Central America, Sri Lanka, India and beyond. Althoug also being observed in women, CKDu concentrates among men in agricultural sectors. Therefore, suspicions fell initially on pesticide exposure, but currently chronic heat stress and dehydration are considered key etiologic factors. Responding to persistent community and scientific concerns about the role of pesticides, we performed a systematic review of epidemiologic studies that addressed associations between any indicator of pesticide exposure and any outcome measure of CKD. Of the 21 analytical studies we identified, seven were categorized as with low, ten with medium and four with relatively high explanation value. Thirteen (62%) studies reported one or more positive associations, but four had a low explanation value and three presented equivocal results. The main limitations of both positive and negative studies were unspecific and unquantified exposure measurement ('pesticides'), the cross-sectional nature of most studies, confounding and selection bias. The four studies with stronger designs and better exposure assessment (from Sri Lanka, India and USA) all showed exposure-responses or clear associations, but for different pesticides in each study, and three of these studies were conducted in areas without CKDu epidemics. No study investigated interactions between pesticides and other concommittant exposures in agricultural occupations, in particular heat stress and dehydration. In conclusion, existing studies provide scarce evidence for an association between pesticides and regional CKDu epidemics but, given the poor pesticide exposure assessment in the majority, a role of nephrotoxic agrochemicals cannot be conclusively discarded. Future research should procure assessment of lifetime exposures to relevant specific pesticides and enough power to look into interactions with other major risk factors, in particular heat stress.