The blood serum concentration of cystatin C (gamma-trace) as a measure of the glomerular filtration rate

Evaluating cystatin-C and monocyte-to-high-density lipoprotein cholesterol ratio as indicators of obstructive sleep apnea severity in male patients

Objectives

This study investigates the association between blood cystatin-C (Cys-C) and monocyte-to-high-density lipoprotein cholesterol ratio (MHR), both established inflammatory markers, with the severity of obstructive sleep apnea (OSA) in male patients.

Methods

A total of 117 male participants who underwent overnight polysomnography (PSG) between February 2019 and December 2022 were included. Based on the apnea-hypopnea index (AHI), participants were categorized into three groups: G1 (AHI < 5 events/hour, n = 9; control group), G2 (5 ≤ AHI < 30 events/hour, n = 32), and G3 (AHI ≥ 30 events/hour, n = 76). Serum Cys-C and MHR levels were measured and analyzed for their correlation with OSA severity. Multivariate logistic regression and receiver operating characteristic (ROC) analyses assessed their diagnostic value, while restricted cubic spline (RCS) analysis examined potential nonlinear relationships.

Results

Cys-C and MHR levels increased with OSA severity and showed significant positive correlations with AHI (Cys-C: r = 0.084, P < 0.05; MHR: r = 0.1286, P < 0.05). In multivariate regression, MHR remained an independent correlate of OSA severity (adjusted OR = 47.130, 95% CI: 1.014-6.692, P = 0.008), whereas Cys-C lost statistical significance after adjusting for confounders. RCS analysis found no significant nonlinear relationship (P > 0.05). ROC analysis showed that combining Cys-C and MHR modestly improved diagnostic accuracy (AUC = 0.6622, 95% CI: 0.554-0.77). Subgroup analysis indicated that severe OSA patients with hypertension had higher Cys-C and MHR levels compared to those without hypertension, though the differences were not statistically significant (P > 0.05).

Conclusions

Cys-C and MHR are positively associated with OSA severity, with MHR emerging as a stronger independent biomarker. Incorporating these markers into OSA risk stratification may enhance clinical assessment and targeted interventions. Future large-scale prospective studies are needed to validate their prognostic value and clinical utility.

Glomerular Filtration Rate (GFR) Estimation with Cystatin C-Past, Present, and Future

BACKGROUND

Cystatin C is a long-established filtration marker which can be used to assess kidney function, but it has been sparingly used for clinical care due to creatinine's role as the primary biomarker for kidney function assessment based on estimated glomerular filtration rate (eGFR).

CONTENT

This review summarizes the evolution of cystatin C's role in kidney disease assessment and highlights new guidelines promoting more widespread use. Specifically, the 2021 National Kidney Foundation and American Society of Nephrology Task Force on Reassessing the Inclusion of Race in Diagnosing Kidney Disease report, and the 2024 Kidney Disease Improving Global Outcomes (KDIGO) Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease (CKD), recommend increased use of cystatin C as an alternative and complementary biomarker for kidney function assessment, since it does not differ by race like creatinine, correlates better with adverse outcomes compared to creatinine, and provides a more accurate eGFR when used in combination with creatinine.

SUMMARY

While robust literature demonstrates improved accuracy with cystatin C-based eGFR (eGFRcys) in certain clinical subpopulations, future research is needed to better understand its performance relative to creatinine-based eGFR (eGFRcr) and measured glomerular filtration rate (mGFR) in additional diverse cohorts, and to achieve assay standardization to match the performance of creatinine assays. Additionally, cystatin C testing availability will need to be broadened from primarily reference laboratories to local laboratories, and partnerships will need to be developed between clinical stakeholders and the laboratory to promote cystatin C's clinical use, to achieve widespread adoption of guideline-recommended eGFR equations.

Electrochemical and optical methods for detection of cystatin C as a biomarker of kidney disease

The kidneys have vital functions in the body, including maintaining homeostasis and blood pressure, controlling water-electrolyte balance, and eliminating metabolic wastes. Early identification of renal dysfunction disease and selection of effective treatment methods reduce mortality in patients. Nowadays, Common indicators of kidney function lack the necessary specificity and sensitivity, but recent studies have reported that cystatin C (CysC) may be an ideal marker for glomerular filtration. CysC, known as a cysteine protease inhibitor, is synthesized by nucleated cells and is easily filtered due to its positive charge and low molecular weight. Also, the synthesis and secretion of CysC is a stable process that is not affected by dietary factors, enhanced protein catabolism, and renal conditions. Various studies have reported that measuring the level of CysC in the body's biological fluids is necessary for the treatment and diagnosis of a wide range of diseases, especially chronic kidney disease (CKD).Despite evidence that positive correlation between the high risk and/or progression of CKD and CysC, it's applied in clinical practice is still rare. Biosensors have been widely developed and researched as an effective method for the pharmaceutical, environmental, and medical fields. Biosensors are designed to create an effective electronic signal commensurate with the concentration of a particular biochemical.Recently, many studies have used biosensor techniques to detect CysC in kidneys and other diseases. In this study, we attempt to examine studies that have used different biosensor techniques for the detect CysC.

Different ways of diagnosing selective glomerular hypofiltration syndromes such as shrunken pore syndrome and the associated increase in mortality

BACKGROUND

In 2015, a selective decrease in the glomerular filtration of middle-sized molecules such as cystatin C compared to small molecules such as creatinine was first described and tentatively termed "Shrunken pore syndrome." Numerous studies have thereafter found an association between this syndrome (defined by a low eGFRcystatin C to eGFRcreatinine ratio) and mortality and morbidity. In 2023, the syndrome was renamed selective glomerular hypofiltration syndromes (SGHS) as shrunken pores are not the only pathophysiological mechanism. Recently, some studies have used the difference between eGFRcystatin C and eGFRcreatinine to describe a similar disorder, and this investigation compares the two measures.

METHODS

Using a cohort of 2781 adults with a median follow-up of 5.6 years, referred for determination of glomerular filtration rate (GFR), estimated GFR (eGFR) was determined using four equations. SGHS was defined using the eGFRdifference and the eGFRratio and association to mortality investigated through adjusted Cox proportional hazard models. From each adjusted regression model, Harrell's C-index and 95% confidence intervals were calculated.

RESULTS

Both measures were associated with mortality. No significant differences concerning hazard ratios or Harrell's C-index were found between the two measures to estimate mortality, and both identified SGHS and increased mortality in a subpopulation of 567 "healthy" individuals with no prior diagnosis and with no kidney disorder according to the kidney disease improving global outcomes-criteria.

CONCLUSION

The eGFRdifference is not superior to the eGFRratio in diagnosing SGHS or estimating mortality. However, as the two measures do not identify the same subpopulation, using them simultaneously might improve risk stratification.

Mendelian randomization study of the relationship between blood and urine biomarkers and lung cancer

Introduction

Identifying suitable biomarkers is crucial for exploring the pathogenesis, early screening, and therapeutic monitoring of lung cancer. This study aims to analyze comprehensively the associations between lung cancer and biomarkers in blood and urine.

Methods

Bidirectional two-sample Mendelian randomization (MR) was used to evaluate the potential causal relationships between blood and urine biomarkers and lung cancer. We obtained Single nucleotide polymorphisms (SNPs) related to lung cancer from the 2021 Finnish database of genome-wide association studies, including small cell lung cancer (SCLC), total non-small cell lung cancer (NSCLC), lung adenocarcinoma (LAC), and lung squamous cell carcinoma (LSCC).Data on blood and urine biomarkers were derived from the UK Biobank cohort, comprising 376,807 participants.

Results

We found a potential inverse causal relationship between total bilirubin and SCLC (β=-0.285, P=0.015, FDR=0.12). Urate was inversely associated with NSCLC (β=-0.158, P=0.004, FDR=0.036*). Serum calcium showed a possible inverse relationship with lung squamous cell carcinoma (β=-0.256, P=0.046, FDR=0.138), while urinary creatinine was positively associated (β=1.233, P=0.024, FDR=0.216). Non-albumin proteins (β=-0.272, P=0.020, FDR=0.180) and total protein (β=-0.402, P=0.009, FDR=0.072) were inversely related to lung squamous cell carcinoma. The AST/ALT ratio was positively associated with lung adenocarcinoma (β=0.293, P=0.009, FDR=0.072). Our reverse Mendelian randomization study found a positive causal association between small cell lung cancer and serum creatinine (β=0.022, P=0.002, FDR=0.018*), while it was inversely associated with the estimated glomerular filtration rate(eGFR)(β=-0.022, P=0.003, FDR=0.027*). A positive causal relationship was also observed with cystatin C (β=0.026, P=0.005, FDR=0.045*) and glycated hemoglobin HbA1c (β=0.013, P=0.014, FDR=0.028*). A negative causal relationship was observed with Gamma_glutamyltransferase (β=-0.013, P=0.019, FDR=0.152). For non-small cell lung cancer, a negative causal relationship was found with albumin (β=-0.024, P=0.002, FDR=0.016*), while a potentially positive causal relationship was observed with cystatin C (β=0.022, P=0.006, FDR=0.054). Possible negative causal relationships were also observed with phosphate (β=-0.013, P=0.008, FDR=0.072) and urinary potassium (β=-0.011, P=0.012, FDR=0.108), while a potential positive causal relationship was observed with C-reactive protein (β=0.013, P=0.040, FDR=0.280).Regarding lung squamous cell carcinoma, an inverse causal relationship was found with eGFR (β=-0.022, P=9.58e-06, FDR=8.62×10-5*), while a positive causal relationship was observed with serum creatinine (β=0.021, P=1.16e-4, FDR=1.05×10-3*). Potential positive causal relationships were observed with Urate (β=0.012, P=0.020, FDR=0.180), urea (β=0.010, P=0.046, FDR=0.141), and glycated hemoglobin HbA1c (β=0.020, P=0.049, FDR P=0.098), whereas a potential negative causal relationship was observed with sex hormone-binding globulin(SHBG) (β=-0.020, P=0.036, FDR=0.108).Lastly, adenocarcinoma was found to have a positive causal association with alkaline phosphatase (β=0.015, P=0.006, FDR=0.033*).

Conclusion

Our study provides a robust theoretical basis for the early screening and therapeutic monitoring of lung cancer and contributes to understanding the pathogenesis of the disease.

Which is the best glomerular filtration marker: Creatinine, cystatin C or both?

BACKGROUND

The glomerular filtration rate (GFR) is estimated by the serum or plasma concentration of creatinine and/or cystatin C using equations that include demographic data. The equations worldwide most widely used are those of the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) consortium and updated in 2021 to remove the Afro-American racial correction factor. In 2021 and then in 2023, the European Kidney Function Consortium also developed equations based on creatinine and cystatin C, usable across the full age spectrum, and constructed by including the Q value (i.e. the median creatinine or cystatin C in healthy men and women, which is customizable for specific populations).

METHODS

The aim of this narrative review is to examine the strengths and weaknesses of each biomarker.

RESULTS

Both biomarkers have non-GFR determinants, namely muscle mass, protein intake and tubular secretion for creatinine; dysthyroidism and systemic corticosteroids for cystatin C, as well as other more debated determinants (diabetes, obesity, proteinuria, inflammatory syndrome). These non-GFR determinants are the reason why no equation based on a single endogenous biomarker has an accuracy within 30% greater than 90% over the entire age spectrum (in at least one patient in 10, estimated GFR is at least 30% higher or at least 30% lower than the measured GFR).

CONCLUSION

Equations combining the two biomarkers provide a better estimate of GFR, particularly in the subgroup of patients whose estimates based on each of the biomarkers are highly discordant. These patients must also be identified as being at increased risk of morbidity, particularly cardiovascular, and mortality.

Newborn glomerular function and gestational particulate air pollution

BACKGROUND

Nephron number variability may hold significance in the Developmental Origins of Health and Disease hypothesis. We explore the impact of gestational particulate pollution exposure on cord blood cystatin C, a marker for glomerular function, as an indicator for glomerular health at birth.

METHODS

From February 2010 onwards, the ENVIRONAGE cohort includes over 2200 mothers giving birth at the East-Limburg hospital in Genk, Belgium. Mothers without planned caesarean section who are able to fill out a Dutch questionnaire are eligible. Here, we evaluated cord blood cystatin C levels from 1484 mother-child pairs participating in the ENVIRONAGE cohort. We employed multiple linear regression models and distributed lag models to assess the association between cord blood cystatin C and gestational particulate air pollution exposure.

FINDINGS

Average ± SD levels of cord blood cystatin C levels amounted to 2.16 ± 0.35 mg/L. Adjusting for covariates, every 0.5 μg/m³ and 5 μg/m³ increment in gestational exposure to black carbon (BC) and fine particulate matter (PM2.5) corresponded to increases of 0.04 mg/L (95% CI 0.01-0.07) and 0.07 mg/L (95% CI 0.03-0.11) in cord blood cystatin C levels (p < 0.01), respectively. Third-trimester exposure showed similar associations, with a 0.04 mg/L (95% CI 0.00-0.08) and 0.06 mg/L (95% CI 0.04-0.09) increase for BC and PM2.5 (p < 0.02). No significant associations were observed when considering only the first and second trimester exposure.

INTERPRETATION

Our findings indicate that particulate air pollution during the entire pregnancy, with the strongest effect sizes from week 27 onwards, may affect newborn kidney function, with potential long-term implications for later health.

FUNDING

Special Research Fund (Bijzonder Onderzoeksfonds, BOF), Flemish Scientific Research Fund (Fonds Wetenschappelijk Onderzoek, FWO), and Methusalem.

Nontargeted Plasma Proteomic Analysis of Renal Disease and Pulmonary Hypertension in Patients with Sickle Cell Disease

Sickle cell disease (SCD) is characterized by red blood cell sickling, vaso-occlusion, hemolytic anemia, damage to multiple organ systems, and, as a result, shortened life expectancy. Sickle cell disease nephropathy (SCDN) and pulmonary hypertension (pHTN) are common and frequently co-occurring complications of SCD; both are associated with markedly accelerated mortality. To identify candidate circulating biomarkers of SCDN and pHTN, we used mass spectrometry to quantify the relative abundance of >1000 proteins in plasma samples from 189 adults with SCD from the Outcome Modifying Genes in SCD (OMG-SCD) cohort (ProteomeXchange identifier PXD048716). Forty-four proteins were differentially abundant in SCDN, most significantly cystatin-C and collagen α-1(XVIII) chain (COIA1), and 55 proteins were dysregulated in patients with SCDN and pHTN, most significantly insulin-like growth factor-binding protein 6 (IBP6). Network analysis identified a module of 133 coregulated proteins significantly associated with SCDN, that was enriched for extracellular matrix proteins, insulin-like growth factor binding proteins, cell adhesion proteins, EGF-like calcium binding proteins, and several cadherin family members. Collectively, these data provide a comprehensive understanding of plasma protein changes in SCDN and pHTN which validate numerous studies of chronic kidney disease and suggest shared profiles of protein disruption in kidney dysfunction and pHTN among SCD patients.

Renal Biomarkers in Heart Failure: Systematic Review and Meta-Analysis

Background

Cystatin C, neutrophil gelatinase-associated lipocalin (NGAL), and kidney injury molecule (KIM)-1 are renal biomarkers increasingly appreciated for their role in the risk stratification and prognostication of heart failure (HF) patients. However, very few have been adopted clinically, owing to the lack of consistency.

Objectives

The authors aimed to study the association between cystatin C, NGAL, and KIM-1 and outcomes, mortality, hospitalizations, and worsening renal function (WRF) in patients with acute and chronic HF.

Methods

We included peer-reviewed English-language articles from PubMed and EMBASE published up to December 2021. We analyzed the above associations using random-effects meta-analysis. Publication bias was assessed using funnel plots.

Results

Among 2,631 articles, 100 articles, including 45,428 patients, met the inclusion criteria. Top-tertile of serum cystatin C, when compared to the bottom-tertile, carried a higher pooled hazard ratio (pHR) for mortality (pHR: 1.59, 95% CI: 1.42-1.77) and for the composite outcome of mortality and HF hospitalizations (pHR: 1.49, 95% CI: 1.23-1.75). Top-tertile of serum NGAL had a higher hazard for mortality (pHR: 2.91, 95% CI: 1.49-5.67) and composite outcome (HR: 4.11, 95% CI: 2.69-6.30). Serum and urine NGAL were significantly associated with WRF, with pHRs of 2.40 (95% CI: 1.48-3.90) and 2.01 (95% CI: 1.21-3.35). Urine KIM-1 was significantly associated with WRF (pHR: 1.60, 95% CI: 1.24-2.07) but not with other outcomes. High heterogeneity was noted between studies without an obvious explanation based on meta-regression.

Conclusions

Serum cystatin C and serum NGAL are independent predictors of adverse outcomes in HF. Serum and urine NGAL are important predictors of WRF in HF.

Association of obstructive sleep apnea and diurnal variation of cystatin C

PURPOSE

Obstructive sleep apnea is a known risk factor for the progression of chronic kidney disease. To find early signs of the progression in subjects with obstructive sleep apnea., we assessed the diurnal variation of kidney biomarkers.

METHODS

A prospective observational study was conducted at Kangwon National University Hospital, Chuncheon, South Korea. All participants underwent in-laboratory polysomnography and phlebotomy in the evening before the polysomnography and in the morning after the polysomnography. Kidney biomarkers, including serum creatinine, blood urea nitrogen, and serum cystatin C, were measured. Delta kidney biomarkers were calculated by subtracting the evening level of the biomarkers from the morning level.

RESULTS

Twenty-six of 50 participants had severe obstructive sleep apnea. Delta cystatin C was significantly correlated with apnea-hypopnea index, oxygen desaturation index, and total arousal index with coefficients of -0.314, -0.323, and -0.289, respectively. In participants without severe obstructive sleep apnea, the morning cystatin C level (0.84 ± 0.11 mg/L) was significantly higher than the evening cystatin C level (0.81 ± 0.11 mg/L) (P = 0.005). With severe obstructive sleep apnea, the cystatin C levels were not different between the morning (0.85 ± 0.11 mg/L) and the evening (0.85 ± 0.10 mg/L).

CONCLUSIONS

Cystatin C level was increased in the morning in participants without severe obstructive sleep apnea, but not in participants with severe obstructive sleep apnea.

Overview of Antibiotic-Induced Nephrotoxicity

Drug-induced nephrotoxicity accounts for up to 60% of cases of acute kidney injury (AKI) in hospitalized patients and is associated with increased morbidity and mortality in both adults and children. Antibiotics are one of the most common causes of drug-induced nephrotoxicity. Mechanisms of antibiotic-induced nephrotoxicity include glomerular injury, tubular injury or dysfunction, distal tubular obstruction from casts, and acute interstitial nephritis (AIN) mediated by a type IV (delayed-type) hypersensitivity response. Clinical manifestations of antibiotic-induced nephrotoxicity include acute tubular necrosis (ATN), AIN, and Fanconi syndrome. Given the potential nephrotoxic effects of antibiotics on critically ill patients, the use of novel biomarkers can provide information to optimize dosing and duration of treatment and can help prevent nephrotoxicity when traditional markers, such as creatinine, are unreliable. Use of novel kidney specific biomarkers, such as cystatin C and urinary kidney injury molecule-1 (KIM-1), may result in earlier detection of AKI, dose adjustment, or discontinuation of antibiotic and development of nonnephrotoxic antibiotics.

Diagnostic challenges of diabetic kidney disease

Diabetic kidney disease (DKD) is one of the most common microvascular complications of both type 1 and type 2 diabetes and the most common cause of the end-stage renal disease (ESRD). It has been evidenced that targeted interventions at an early stage of DKD can efficiently prevent or delay the progression of kidney failure and improve patient outcomes. Therefore, regular screening for DKD has become one of the fundamental principles of diabetes care. Long-established biomarkers such as serum-creatinine-based estimates of glomerular filtration rate and albuminuria are currently the cornerstone of diagnosis and risk stratification in routine clinical practice. However, their immanent biological limitations and analytical variations may influence the clinical interpretation of the results. Recently proposed new predictive equations without the variable of race, together with the evidence on better accuracy of combined serum creatinine and cystatin C equations, and both race- and sex-free cystatin C-based equation, have enabled an improvement in the detection of DKD, but also require the harmonization of the recommended laboratory tests, wider availability of cystatin C testing and specific approach in various populations. Considering the complex pathophysiology of DKD, particularly in type 2 diabetes, a panel of biomarkers is needed to classify patients in terms of the rate of disease progression and/or response to specific interventions. With a personalized approach to diagnosis and treatment, in the future, it will be possible to respond to DKD better and enable improved outcomes for numerous patients worldwide.

The estimation of glomerular filtration in acute and critical illness: Challenges and opportunities

Recent events have made it apparent that the creatinine based estimating equations for glomerular filtration have their flaws. Some flaws have been known for some time; others have prompted radical modification of the equations themselves. These issues persist in part owing to the behaviour of the creatinine molecule itself, particularly in acute and critical illness. There are significant implications for patient treatment decisions, including drug and fluid therapies and choice of imaging modality (contrast vs. non-contrast CT scan for example). An alternative biomarker, Cystatin C, has been used with some success both alone and in combination with creatinine to help improve the accuracy of particular estimating equations. Problems remain in certain circumstances and costs may limit the more widespread use of the alternative assay. This review will explore both the historical and more recent evidence for glomerular filtration estimation, including options to directly measure glomerular filtration (rather than estimate), perhaps the holy grail for both Biochemistry and Nephrology.

Serum cystatin C and CRP are early predictive biomarkers for emergence of hypoxia in COVID-19

BACKGROUND

In Japan, during the coronavirus disease 2019 (COVID-19) pandemic, patients with non-hypoxia are recommended to recuperate at home or in pre-hospital facilities. However, it was observed that unexpected hypoxia may occur and become severe subsequently in patients whose symptoms were initially expected to improve naturally. The aim of this study is to validate biomarkers that can predict at an early stage the emergence of hypoxia in COVID-19 patients without hypoxia.

METHODS

We retrospectively enrolled 193 patients with COVID-19, excluding patients with hypoxia and severe disease from the onset. Participants were classified into two groups according to the emergence of hypoxia during the clinical course, and the laboratory data were compared to identify biomarkers that could predict early the emergence of hypoxia.

RESULTS

The areas under the curve for serum cystatin C (CysC) and C-reactive protein (CRP) levels for the emergence of hypoxia during the clinical course were higher than those for other biomarkers (CysC, 0.84 and CRP, 0.83). Multivariate analysis showed that high serum CysC and CRP levels were associated with the emergence of hypoxia during the clinical course.

CONCLUSIONS

Elevated serum CysC and CRP levels were associated with the emergence of hypoxia during the clinical course in COVID-19 patients without hypoxia. These findings may help determine the need for hospitalization in initially non-hypoxic COVID-19 patients.

Flash Characterization of Smartphones Used in Point-of-Care Diagnostics

Rapidly growing interest in smartphone cameras as the basis of point-of-need diagnostic and bioanalytical technologies increases the importance of quantitative characterization of phone optical performance under real-world operating conditions. In the context of our development of lateral-flow immunoassays based on phosphorescent nanoparticles, we have developed a suite of tools for characterizing the temporal and spectral profiles of smartphone torch and flash emissions, and their dependence on phone power state. In this work, these tools are described and documented to make them easily available to others, and demonstrated by application to characterization of Apple iPhone 5s, iPhone 6s, iPhone 8, iPhone XR, and Samsung Note8 flash performance as a function of time and wavelength, at a variety of power settings. Flash and torch intensity and duration vary with phone state and among phone models. Flash has high variability when the battery charge is below 10%, thus, smartphone-based Point-of-Care (POC) tests should only be performed at a battery level of at least 15%. Some output variations could substantially affect the results of assays that rely on the smartphone flash.

Effect of Cardiac Rehabilitation on Glomerular Filtration Rate Using Serum Cystatin C Concentration in Patients With Cardiovascular Disease and Renal Dysfunction

PURPOSE

Among patients with chronic kidney disease (CKD), little is known about whether the effect of cardiac rehabilitation (CR) on renal function differs across baseline estimated glomerular filtration rate using the serum concentration of cystatin C (eGFRcys). The aim of this study was to evaluate the effect of CR on renal function in patients with CKD.

METHODS

We performed a retrospective cohort study of patients with CKD (15 ≤ eGFRcys < 60 mL/min/1.73 m2) who participated in our CR program for cardiovascular disease. First, the patients were divided into three groups according to the baseline severity of the eGFRcys: G3a, G3b, and G4 groups. We compared the eGFRcys before and after the CR in each group. Second, to determine the association of baseline eGFRcys with the effect of CR, we fitted a linear regression model using the percent change in the eGFRcys (%ΔeGFRcys) as an outcome.

RESULTS

Of the 203 patients, 122 were in G3a, 60 were in G3b, and 21 were in G4 groups. The mean improvement of eGFRcys in each group was 1.3, 3.1, and 4.8 mL/min/1.73 m2, respectively. The %ΔeGFRcys was larger among patients with lower baseline eGFRcys (0.47% greater improvement of %ΔeGFRcys/one lower baseline eGFRcys; 95% CI, 0.23-0.72%). This association remained significant after adjustment for potential confounders (0.63% greater improvement of %ΔeGFRcys/one lower baseline eGFRcys; 95% CI, 0.35-0.91%).

CONCLUSIONS

The effect of CR on renal function was greater in patients with worse renal dysfunction measured by eGFRcys. A CR program could be useful for patients with severe renal dysfunction and it might have a beneficial effect on their renal function.

Cystatin C-based equations for estimating glomerular filtration rate do not require race or sex coefficients

Estimation or measurement of glomerular filtration rate (GFR) is generally required for optimal treatment of patients. Plasma creatinine has been used for estimation of GFR since 1926 and plasma cystatin C since 1979. The creatinine level is strongly dependent upon muscle mass and as the average muscle mass of different populations may vary, creatinine-based GFR-estimating equations have since 1999 used more than 10 different race coefficients to improve the diagnostic performance of such equations. But 'race' cannot be determined by biological measurements and is thus an ill-defined biological entity and controversial as it involves self-reporting and social considerations. In contrast, cystatin C-levels are virtually independent of muscular mass and cystatin C-based GFR-estimating equations do not require race coefficients for reliable estimation of GFR. The use of cystatin C-based GFR-estimating equations, alone or in conjunction with creatinine-based GFR-estimating equations, is therefore highly recommended to eliminate the use of race coefficients in estimating GFR. Although sex is a more biology-oriented parameter than race, sex terms may in some cases be controversial, involving self-reporting and social considerations. However, sex terms are not required for adequate estimation of GFR using cystatin C-based equations.

Serum Cystatin C in Chronic Kidney Disease: A Case-Control Study

Background: Chronic kidney disease (CKD) is a major public health concern in recent years mainly due to its adverse clinical outcomes. It is most commonly attributed to diabetes mellitus (DM) and hypertension (HTN). Among the several novel biomarkers discovered to detect impaired renal function, serum cystatin C (SCysC) has gained importance. Objectives: The aim of the study was to compare SCysC and serum creatinine (SCr) in CKD subjects and apparently healthy controls. Methods: This case-control study comprising of 120 diagnosed cases of CKD and 40 controls was conducted at a tertiary care hospital. SCr and SCysC levels were estimated using modified Jaffe’s method and particle enhanced immunoturbidimetric method, respectively. Estimated glomerular filtration rate (eGFR) was calculated using CKD EPI formula. Comparison of SCr and SCysC between cases and controls was done using Mann Whitney U test. Pearson’s correlation test was used to study the correlation between variables. Statistical significance was considered at P<0.05. Results: Both SCr and SCysC levels were higher in cases compared to controls (P<0.001). In the group comprising of Stage 1 and Stage 2 CKD subjects, all the subjects showed normal SCr levels, while 96.8% of the subjects showed elevated SCysC levels. SCysC (r=-0.800) showed better correlation than SCr (r=-0.724) with eGFR (P<0.001). A strong correlation was found between SCysC and SCr levels (r=-0.887, P<0.001). Conclusion: SCysC is a good indicator of renal dysfunction and may be used to screen patients with long duration of DM or HTN for CKD.

Kidney disease risk factors do not explain impacts of low dietary protein on kidney function and structure

The kidneys balance many byproducts of the metabolism of dietary components. Previous studies examining dietary effects on kidney health are generally of short duration and manipulate a single macronutrient. Here, kidney function and structure were examined in C57BL/6J mice randomized to consume one of a spectrum of macronutrient combinations (protein [5%–60%], carbohydrate [20%–75%], and fat [20%–75%]) from weaning to late-middle age (15 months). Individual and interactive impacts of macronutrients on kidney health were modeled. Dietary protein had the greatest influence on kidney function, where chronic low protein intake decreased glomerular filtration rates and kidney mass, whereas it increased kidney immune infiltration and structural injury. Kidney outcomes did not align with cardiometabolic risk factors including glucose intolerance, overweight/obesity, dyslipidemia, and hypertension in mice with chronic low protein consumption. This study highlights that protein intake over a lifespan is an important determinant of kidney function independent of cardiometabolic changes.

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Chronic high macronutrient intake from any source increases kidney function (GFR)

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Low protein intake led to greater kidney tubular structural injury and inflammation

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Lower protein intake decreased kidney mass and glomerular filtration capacity

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Kidney outcomes did not align with longevity or cardiometabolic outcomes

Age-Related Change in Hepatic Clearance Inferred from Multiple Population Pharmacokinetic Studies: Comparison with Renal Clearance and Their Associations with Organ Weight and Blood Flow

OBJECTIVE

This study aimed to examine the magnitude of age-related change in hepatic clearance by integrating the data of multiple drugs and to compare this with renal clearance, considering associations with age-related changes in organ weight and blood flow.

METHODS

The results of multiple population pharmacokinetic analyses that detected age-related clearance changes in hepatically eliminated drugs were collected. The relationship between hepatic clearance of the unbound drug and age was then analyzed using the nonlinear least-squares method, adjusting for interdrug differences. The obtained change in hepatic clearance was compared with age-related changes in liver weight and hepatic blood flow in Japanese and Westerners. For comparison, the changes in renal clearance were analyzed similarly.

RESULTS

In total, 18 drugs were analyzed. The hepatic unbound clearance decreased by 32% at age 80 years and by 40% at age 90 years, compared with age 40 years, suggesting that it decreased by 0.80% per year with aging. The rate of the decrease was consistent with decreases in hepatic weight per person or blood flow per person, regardless of ethnicity and sex. Since age-related change in body weight varied somewhat by sex or ethnicity, hepatic weight per body weight was less consistent to account for age-related change in hepatic clearance. As for an index of renal clearance, the changes in inulin clearance with age were similar to those in renal blood flow, with a decrease of 0.97% per year from the age of 40 years.

CONCLUSIONS

Hepatic clearance consistently decreased by 0.80% per year from the age of 40 years, with aging for multiple drugs analyzed in this study. Changes in organ weight and blood flow are considered to be primarily responsible for the age-related changes in hepatic and renal clearance.

Role of Cystatin C in Predicting Disease Activity and Flare-Up in Systemic Lupus Erythematosus: A Longitudinal Follow-Up Study

Background:

We aimed to determine the sensitivity of serum cystatin C (Cys-C) in predicting lupus flare-up.

Methods:

In a longitudinal study, 77 patients were followed-up for up to 15 months. Cys-C, physician global assessment (PGA), and lupus activity index (SLEDAI) were recorded during each visit. Flare-up was defined as an increase ≥4 scores in SLEDAI compared to the last visit. The predictability of flare-up by Cys-C was evaluated by generalized linear-mixed effect model (GLMM) and generalized estimating equation (GEE). Predictive power of Cys-C, SLEDAI, and PGA was compared by the area under the curves (AUC) and application of receiver operating characteristic (ROC) curves.

Results:

Lupus flare-up was observed in 14 out of 77 patients on the 1^st visit, 3 out of 41 patients on the 2^nd visit, 2 out of 26 patients on the 3^rd visit, 1 out of 14 patients on the 4^th visit, and 1 out of 3 patients on the 5^th visit. Mean Cys-C levels in patients with flare-up vs. those with no flare-up in the 1^st, 2^nd, and 3^rd visits were 1769 vs. 1603 (P = 0.6), 5701 vs. 2117 (p = 0.2) and 1409 vs. 1731 (p = 0.9), respectively. Cys-C had lower predictive power than PGA and SLEDAI for either flare-up, active nephritis or SLEDAI in GLMM/GEE models. Cys-C also showed lower sensitivity (AUC = 0.701, 95%CI = 0.579-0.823, P = 0.003) than PGA and SLEDAI, to distinguish patients prone to flare-ups.

Conclusions:

Although Cys-C had some sensitivity for predicting flare-up, active nephritis or SLEDAI, its sensitivity was lower than that in PGA and SLEDAI.

Correlation of Serum Cystatin C with Renal Function in Gout Patients with Renal Injury

The gout-induced continuous deposition of urate in the kidney tissues is the main cause of renal injury, for which cystatin C (Cys C) is an important indicator. This research analyzed the correlation between general renal injury indicators and serum Cys C level, and further investigated the potential of Cys C in renal injury diagnosis. A total of 140 gout patients with renal injury (GRI) were recruited and grouped by their glomerular filtration rate (GFR). Urea nitrogen, uric acid, creatinine, and Cys C levels in the serum were evaluated. The diagnostic efficacy of serum Cys C was evaluated by the nonparametric receiver operating characteristic analysis. Serum Cys C level was increased with decreased GFR in GRI. Urea nitrogen, uric acid, and creatinine levels in the serum showed positive correlations with Cys C level. The area under the curve for serum Cys C was 0.8589 (P < 0.001). In conclusion, this research demonstrated that the serum Cys C level was a precise diagnostic marker for GFR and renal damage evaluation, and showed a significant diagnostic value for renal injury in patients with gout.

Predictors associated with sickle cell nephropathy: a systematic review

INTRODUCTION

Sickle cell anemia affects more than 30 million people worldwide. Chronic kidney disease develops in 40% of individuals. The death rate of patients with sickle nephropathy is still high, with little known predictors related to its development. To answer the question "What predictors are associated with the onset of chronic kidney disease in patients with sickle cell anemia?", this article seeks to contribute to a better understanding of sickle nephropathy, making possible a new look at the sickle cell anemia and its kidney complications.

METHODS

A systematic review was developed, using the PRISMA recommendation, for cohort studies on predictors related to the outcome of sickle nephropathy in patients with sickle cell anemia.

RESULTS

Initially 321 studies were identified in Pubmed, of which six were selected to compose this systematic review. Lower hemoglobin levels, increased ages and albuminuria were the most pointed predictors associated with chronic kidney disease.

CONCLUSION

The main predictors associated with the development of chronic kidney disease in individuals with sickle cell anemia were lower hemoglobin levels, increased ages, and albuminuria. New studies evaluating predictors for the development of chronic kidney disease in sickle cell anemia are needed to better understand its installation and prevent its progression.

Current knowledge about biomarkers of acute kidney injury in liver cirrhosis

Acute kidney injury (AKI) is common in advanced cirrhosis. Prerenal azotemia, hepatorenal syndrome, and acute tubular necrosis are the main causes of AKI in patients with cirrhosis. Evaluation of renal function and differentiation between functional and structural kidney injury are important issues in the management of cirrhosis. However, AKI in cirrhosis exists as a complex clinical spectrum rather than concrete clinical entity. Based on current evidence, changes in serum creatinine (Cr) levels remain the most appropriate standard for defining AKI in cirrhosis. However, serum Cr has a limited role in assessing renal function in this population. This review examines previous studies that investigated the ability of recent biomarkers for AKI in cirrhosis from the perspective of earlier and accurate diagnosis, classification of AKI phenotype, and prediction of clinical outcomes. Serum cystatin C and urine neutrophil gelatinase-associated lipocalin have been extensively studied in cirrhosis, and have facilitated improved diagnosis and prognosis prediction in patients with AKI. In addition, urine N-acetyl-β-D-glucosaminidase, interleukin 18, and kidney injury molecule 1 are other promising biomarkers for advanced cirrhosis. However, the clinical significance of these markers remains unclear because there are no cut-off values defining the normal range and differentiating phenotypes of AKI. In addition, AKI has been defined in terms of serum Cr, and renal biopsy-the gold standard-has not been carried out in most studies. Further discovery of innovate biomarkers and incorporation of various markers could improve the diagnosis and prognosis prediction of AKI, and will translate into meaningful improvements in patient outcomes.

Potential relationship between eGFRcystatin C /eGFRcreatinine -ratio and glomerular basement membrane thickness in diabetic kidney disease

Diabetic kidney disease (DKD) is a leading cause of end-stage renal disease and renal replacement therapy worldwide. A pathophysiological hallmark of DKD is glomerular basal membrane (GBM) thickening, whereas this feature is absent in minimal change disease (MCD). According to fundamental transport physiological principles, a thicker GBM will impede the diffusion of middle-molecules such as cystatin C, potentially leading to a lower estimated GFR (eGFR) from cystatin C compared to that of creatinine. Here we test the hypothesis that thickening of the glomerular filter leads to an increased diffusion length, and lower clearance, of cystatin C. Twenty-nine patients with a kidney biopsy diagnosis of either DKD (n = 17) or MCD (n = 12) were retrospectively included in the study. GBM thickness was measured at 20 separate locations in the biopsy specimen and plasma levels of cystatin C and creatinine were retrieved from health records. A modified two-pore model was used to simulate the effects of a thicker GBM on glomerular water and solute transport. The mean age of the patients was 52 years, and 38% were women. The mean eGFRcystatin C /eGFRcreatinine -ratio was 74% in DKD compared to 98% in MCD (p < 0.001). Average GBM thickness was strongly inversely correlated to the eGFRcystatin C /eGFRcreatinine -ratio (Pearson's r = -0.61, p < 0.01). Two-pore modeling predicted a eGFRcystatin C /eGFRcreatinine -ratio of 78% in DKD. We provide clinical and theoretical evidence suggesting that thickening of the glomerular filter, increasing the diffusion length of cystatin C, lowers the eGFRcystatin C /eGFRcreatinine -ratio in DKD.

Assessment of renal function using cystatin C and creatinine in Saudi patients after transplantation

Background:

Rapid and accurate assessment of kidney function in patients after transplantation is of utmost importance. The aim of this study was to compare the relationships of serum creatinine and serum cystatin C with an estimated glomerular filtration rate (eGFR) in kidney transplants Saudi patients after a certain period of transplantation.

Materials and Methods:

In this prospective study, 127 patients were categorized into three groups based on their length of survival after kidney transplantation; <1 year, from 1 to 5 years, and above 5 years after transplantation. Results of cystatin C and creatinine levels were compared by eGFR derived from estimation equation chronic kidney disease epidemiology collaboration.

Results:

In the three assessed periods, the mean (standard deviation) cystatin C level was 1.72 (0.57), 1.59 (0.64), and 1.82 (0.82), respectively, being highest after 5 years of transplantation, normal in 9.40%, and elevated in 90.60% of the participants, while creatinine level, decreased from 1.57 (0.53) to 1.52 (0.64) in 1–5 years, then it became the highest at 1.75 (0.69) in more than 5 years. The mean was normal in 21.30% and elevated in 78.70% of the patients. Both serum creatinine and cystatin C levels were negatively correlated with posttransplantation time in kidney transplant patients.

Conclusion:

The cystatin C level was statistically significantly higher after 5 years of transplantation. It is a better parameter to rule out renal dysfunction after transplantation.

Serum cystatin C unmasks renal dysfunction in cirrhosis and performs better in estimation of glomerular filtration rate

In this study, we aimed to measure glomerular filtration rate (mGFR) using ⁹⁹Tc DTPA in patients with Child-Pugh C cirrhosis and normal serum creatinine levels; and to compare the performance of creatinine and cystatin C-based equations [estimated GFRs (eGFRs)] to ⁹⁹TcDTPA GFR in the same group. We selected a group of 65 consecutive patients with advanced liver cirrhosis and apparently normal renal function by serum creatinine alone. Patients with confounding and reversible factors were excluded. Demographic data, blood, urine, and imaging tests along with simultaneous measurement of serum creatinine and cystatin C were analyzed. The GFR was measured by ⁹⁹Tc DTPAscintigraphy (mGFR) in 41 patients. We compared the performance of chronic kidney disease epidemiology collaboration (CKD-EPI-creatinine, CKD-EPI-cystatinC, CKD-EPI-creatinine-cystatinC) and Modification of Diet in Renal Disease equation equations for bias (mean difference), precision (root mean square error), and accuracy (P10 and P30). Bland-Altman plots were used to show the agreement of eGFR and mGFR. Twenty-five out of 41 patients (61%) had significant renal dysfunction (GFR ≤60 mL/min/ 1.73m²) by ⁹⁹TcDTPA in our study and three patients were already in Stage 4 CKD. Unlike serum creatinine, serum cystatin C values were deranged in these patients. Among all GFR estimating formulae, CKD-EPI-creatinine-cystatinC combined equation had the least bias (-2.3), superior precision (7.1), highest P30 accuracy (78%), good sensitivity (87.5%), and best specificity (96%) in our study. Two-thirds of patients with cirrhosis had significant renal impairment despite having normal serum creatinine. Isolated serum creatinine values are misleading in cirrhosis. Cystatin C unmasks renal dysfunction in these patients. CKD-EPI-creatinine-cystatinC equation showed the best correlation and accuracy with ⁹⁹TcDTPA GFR in our study. Creatinine based GFR estimation is fallacious in cirrhosis. Cystatin C and equations based on it may be worthwhile in liver disease.

Association of Oral Status and Early Primary Hypertension Biomarkers among Children and Adolescents

The aim of this case-control study was the evaluation of the association between biomarkers of early primary arterial hypertension (HA) and oral diseases among children and adolescents. Material and methods. Subjects suspected of primary HA (n = 180) underwent a complex evaluation of their vascular status: blood pressure, heart rate, vascular stiffness, sympathetic activity in a 24 h ambulatory examination, followed by measurement of serum uric acid (UA), cystatin C, and creatinine. This procedure allowed the identification of children with primary (n = 58) and secondary HA (n = 74), as well as of children with normal arterial blood pressure, who served as a control group (n = 48). All subjects with secondary HA were excluded from further investigation. Oral examination included the measurement of caries intensity (using the decayed, missing, filled index for permanent teeth DMFT /primary teeth dmft), bacterial plaque (by the plaque control record index, PCR%), and gingivitis (by the bleeding on probing index, BOP%). For statistical analysis, a linear regression model and Spearman rank correlation were used. Results. UA, cystatin C, and creatinine were not altered in the HA group. However, the number of decayed permanent teeth (DT) and the DMFT, PCR%, and BOP% indexes were significantly higher in the primary HA group compared to the control group (p = 0.0006; p = 0.02; p = 0.0009; p = 0.003). Our results are not sufficient to prove the important role of caries and gingival inflammation in the modulation of HA symptoms, although they prove the association of oral diseases with primary HA symptoms. This may indicate future strategies for preventive measures for hypertensive children and adolescents.

Predictive value of serum cystatin C for risk of mortality in severe and critically ill patients with COVID-19

BACKGROUND

The outbreak of coronavirus disease 2019 (COVID-19) has rapidly evolved into a global pandemic. COVID-19 is clinically categorized into mild, moderate, severe, and critical illness. Acute kidney injury is an independent risk factor for poor prognosis in patients with. Serum cystatin C (sCys C) is considered a more sensitive biomarker for early renal insufficiency than conventional indicators of renal function. Early detection of risk factors that affect the prognosis of severe and critically ill patients while using active and effective treatment measures is very important and can effectively reduce the potential mortality rate.

AIM

To determine the predictive value of sCys C for the prognosis of patients with COVID-19.

METHODS

The clinical data of 101 severe and critically ill patients with COVID-19 at a designated hospital in Wuhan, Hubei Province, China were analyzed retrospectively. According to the clinical outcome, the patients were divided into a discharge group (64 cases) and a death group (37 cases). The general information, underlying diseases, and laboratory examination indexes of the two groups were compared. Multivariate Cox regression was used to explore the relationship between sCys C and prognosis. The receiver operating characteristic (ROC) curve was used to demonstrate the sensitivity and specificity of sCys C and its optimal cut-off value for predicting death.

RESULTS

There were significant differences in age, sCys C, creatinine, C-reactive protein, serum albumin, creatine kinase-MB, alkaline phosphatase, lactate dehydrogenase, neutrophil count, and lymphocyte count between the two groups (P < 0.001). Multivariate logistic regression analysis showed that sCys C was an independent risk factor for death in patients with COVID-19 (Odds ratio = 1.812, 95% confidence interval [CI]: 1.300-2.527, P < 0.001). The area under the ROC curve was 0.755 (95%CI: 1.300-2.527), the cut-off value was 0.80, the specificity was 0.562, and the sensitivity was 0.865.

CONCLUSION

sCys C is an independent risk factor for death in patients with COVID-19. Patients with a sCys C level of 0.80 mg/L or greater are at a high risk of death.

Mechanism-based modeling of the effect of a novel inhibitor of vascular adhesion protein-1 on albuminuria and renal function markers in patients with diabetic kidney disease

The vascular adhesion protein-1 (VAP-1) inhibitor ASP8232 reduces albuminuria in patients with type 2 diabetes and chronic kidney disease. A mechanism-based model was developed to quantify the effects of ASP8232 on renal markers from a placebo-controlled Phase 2 study in diabetic kidney disease with 12 weeks of ASP8232 treatment. The model incorporated the available pharmacokinetic, pharmacodynamic (plasma VAP-1 concentration and activity), serum and urine creatinine, serum cystatin C, albumin excretion rate, urinary albumin-to-creatinine ratio, and urine volume information in an integrated manner. Drug-independent time-varying changes and different drug effects could be quantified for these markers using the model. Through simulations, this model provided the opportunity to dissect the relationship and longitudinal association between the estimated glomerular filtration rate and albuminuria and to quantify the pharmacological effects of ASP8232. The developed drug-independent model may be useful as a starting point for other compounds affecting the same biomarkers in a similar time scale.

Discrepant glomerular filtration rate trends from creatinine and cystatin C in patients with chronic kidney disease: results from the KNOW-CKD cohort

Background

Serum creatinine (Cr) and cystatin C (CysC) can both be used to estimate glomerular filtration rate (eGFR_Cr and eGFR_CysC). However, certain conditions may cause discrepancies between eGFR trends from Cr and CysC, and these remain undetermined in patients with chronic kidney disease (CKD).

Methods

A total of 1069 patients from the Korean CKD cohort (KNOW-CKD), which enrolls pre-dialytic CKD patients, whose Cr and CysC had been followed for more than 4 years were included in the sample. We performed trajectory analysis using latent class mixed modeling and identified members of the discrepancy group when patient trends between eGFR_Cr and eGFR_CysC differed. Multivariate logistic analyses with Firth’s penalized likelihood regression models were performed to identify conditions related to the discrepancy.

Results

Trajectory patterns of eGFR_Cr were classified into three groups: two groups with stable eGFR_Cr (stable with high eGFR_Cr and stable with low eGFR_Cr) and one group with decreasing eGFR_Cr. Trajectory analysis of eGFR_CysC also showed similar patterns, comprising two groups with stable eGFR_CysC and one group with decreasing eGFR_CysC. Patients in the discrepancy group (decreasing eGFR_Cr but stable & low eGFR_CysC; n = 55) were younger and had greater proteinuria values than the agreement group (stable & low eGFR_Cr and eGFR_CysC; n = 706), differences that remained consistent irrespective of the measurement period (4 or 5 years).

Conclusions

In the present study, we identify conditions related to discrepant trends of eGFR_Cr and eGFR_CysC. Clinicians should remain aware of such potential discrepancies when tracing both Cr and CysC.

Shrunken pore syndrome - a common kidney disorder with high mortality. Diagnosis, prevalence, pathophysiology and treatment options

Invasive studies show that the glomerular sieving coefficients for 5-30 kDa plasma proteins in the human kidney may be selectively reduced compared to those for small molecules < 0.9 kDa, commonly used to measure glomerular filtration rate (GFR). Identification of this pathophysiological state, called shrunken pore syndrome (SPS), can easily and non-invasively be done by comparing estimations of GFR using cystatin C (13.3 kDa) and creatinine (0.113 kDa). SPS is present if the estimate of GFR using cystatin C is lower than 60 or 70% of the estimate using creatinine in the absence of non-renal influences on cystatin C or creatinine. All studies of SPS show that the 3- or 5-year mortality is strongly increased and high hazard ratios for mortality associated with SPS have been observed for many different patient cohorts, including cohorts with normal measured GFR, no albuminuria and no diagnosis. The prevalence of SPS in the cohorts so far investigated is between 0.2 and 36%. Proteome studies of SPS demonstrate that the high mortality associated with the syndrome might be caused by the accumulation of 10-30 kDa signalling proteins promoting development of atherosclerosis and thus suggesting use of monoclonal antibodies to reduce the levels of the most detrimental signalling proteins as a treatment option. The KDIGO recommendations for classification of chronic kidney disease (CKD) comprise determination, or estimation, of GFR and analysis of albuminuria and therefore cannot identify a large fraction of the patients with SPS. The high prevalence and mortality of SPS and the possible treatment options strongly suggest that the KDIGO recommendations should be expanded to include determination of cystatin C to be able to identify all patients with SPS.

Current Status of Novel Biomarkers for the Diagnosis of Acute Kidney Injury: A Historical Perspective

Acute kidney injury (AKI) is a common and serious medical condition associated with significant increases in morbidity, mortality, and cost of care. Because of the high incidence and poor outcomes associated with AKI, there has been significant interest in the development of new therapies for the prevention and treatment of the disease. A lack of efficacy in drug trials led to the concern that AKI was not being diagnosed early enough for an effective intervention and that a rise in serum creatinine itself is not a sensitive-enough marker. Researchers have been searching for novel biomarkers that can not only assess a decline in kidney function but also demonstrate structural damage to the kidney and at time points earlier than increases in serum creatinine measurements allow. Over the past 10 years, there have been 3300 new publications and hundreds of new biomarkers investigated, yet concern still remains regarding AKI biomarker performance. The AKI biomarkers are yet to be widely utilized in clinical practice, leading some to question whether AKI biomarkers will ever reach their initial promise. However, we believe that biomarkers are an important part of current and future AKI research and clinical management. In this review, we compare the historical contexts of acute myocardial ischemia and AKI biomarker development to illustrate the progress that has been made within AKI biomarker research in a relatively short period of time and also to point out key differences between the disease processes that have been barriers to widespread AKI biomarker adoption. Finally, we discuss potential paths by which biomarkers can lead to appropriate AKI treatment responses that lower morbidity and mortality.

Biomarkers of Drug-Induced Kidney Toxicity

Blood urea nitrogen and serum creatinine are imperfect markers of kidney function because they are influenced by many renal and nonrenal factors independent of kidney function. A biomarker that is released directly into the blood or urine by the kidney in response to injury may be a better early marker of drug-induced kidney toxicity than blood urea nitrogen and serum creatinine. Urine albumin and urine protein, as well as urinary markers kidney injury molecule-1 (KIM-1), β2-microglobulin (B2M), cystatin C, clusterin, and trefoil factor-3 (TFF-3) have been accepted by the Food and Drug Administration and European Medicines Agency as highly sensitive and specific urinary biomarkers to monitor drug-induced kidney injury in preclinical studies and on a case-by-case basis in clinical trials. Other biomarkers of drug-induced kidney toxicity that have been detected in the urine of rodents or patients include IL-18, neutrophil gelatinase-associated lipocalin, netrin-1, liver-type fatty acid-binding protein (L-FABP), urinary exosomes, and TIMP2 (insulin-like growth factor-binding protein 7)/IGFBP7 (insulin-like growth factor-binding protein 7), also known as NephroCheck, the first Food and Drug Administration-approved biomarker testing platform to detect acute kidney injury in patients. In the future, a combined use of functional and damage markers may advance the field of biomarkers of drug-induced kidney toxicity. Earlier detection of drug-induced kidney toxicity with a kidney-specific biomarker may result in the avoidance of nephrotoxic agents in clinical studies and may allow for earlier intervention to repair damaged kidneys.

Glomerular Filtration Rate Estimation by a Novel Numerical Binning-Less Isotonic Statistical Bivariate Numerical Modeling Method

Statistical bivariate numerical modeling is a method to infer an empirical relationship between unpaired sets of data based on statistical distributions matching. In the present paper, a novel efficient numerical algorithm is proposed to perform bivariate numerical modeling. The algorithm is then applied to correlate glomerular filtration rate to serum creatinine concentration. Glomerular filtration rate is adopted in clinical nephrology as an indicator of kidney function and is relevant for assessing progression of renal disease. As direct measurement of glomerular filtration rate is highly impractical, there is considerable interest in developing numerical algorithms to estimate glomerular filtration rate from parameters which are easier to obtain, such as demographic and `bedside’ assays data.

Comparison of the diagnostic value of symmetric dimethylarginine, cystatin C, and creatinine for detection of decreased glomerular filtration rate in dogs

BACKGROUND

Early detection of decreased glomerular filtration rate (GFR) in dogs is challenging. Current methods are insensitive and new biomarkers are required.

OBJECTIVE

To compare overall diagnostic performance of serum symmetric dimethylarginine (SDMA) and serum cystatin C to serum creatinine, for detection of decreased GFR in clinically stable dogs, with or without chronic kidney disease (CKD).

ANIMALS

Ninety-seven client-owned dogs: 67 dogs with a diagnosis or suspicion of CKD and 30 healthy dogs were prospectively included.

METHODS

Prospective diagnostic accuracy study. All dogs underwent physical examination, systemic arterial blood pressure measurement, urinalysis, hematology and blood biochemistry analysis, cardiac and urinary ultrasound examinations, and scintigraphy for estimation of glomerular filtration rate (mGFR). Frozen serum was used for batch analysis of SDMA and cystatin C.

RESULTS

The area under the curve of creatinine, SDMA, and cystatin C for detection of an mGFR <30.8 mL/min/L was 0.98 (95% confidence interval [CI], 0.93-1.0), 0.96 (95% CI, 0.91-0.99), and 0.87 (95% CI, 0.79-0.93), respectively. The sensitivity of both creatinine and SDMA at their prespecified cutoffs (115 μmol/L [1.3 mg/dL] and 14 μg/dL) for detection of an abnormal mGFR was 90%. The specificity was 90% for creatinine and 87% for SDMA. When adjusting the cutoff for cystatin C to correspond to a diagnostic sensitivity of 90% (0.49 mg/L), specificity was lower (72%) than that of creatinine and SDMA.

CONCLUSIONS AND CLINICAL IMPORTANCE

Overall diagnostic performance of creatinine and SDMA for detection of decreased mGFR was similar. Overall diagnostic performance of cystatin C was inferior to both creatinine and SDMA.

Evaluation of Renal Function in Obese Children and Adolescents Using Serum Cystatin C Levels, Estimated Glomerular Filtration Rate Formulae and Proteinuria: Which is most Useful?

Objective

There is a growing interest in the relationship between obesity and renal damage. The effect of obesity on renal function in children and adolescents has not been adequately investigated. In addition, there is no complete consensus on the reliability of various renal function parameters. The primary goal of this study was to evaluate renal function in obese children and adolescents using glomerular filtration rate (GFR), cystatin C, and creatinine (Cr)-derived formulas. We also compared classical GFR measurement methods with methods based on bioimpedance analysis-derived body cell mass (BCM).

Methods

We enrolled 108 obese and 46 healthy subjects aged 6-18 years. Serum cystatin C, serum Cr, 24-hour proteinuria, Cr clearance, and GFR were evaluated in both groups. Estimated GFR was measured with Cr-based, cystatin C-based, combined (cystatin C and Cr) and BCM-based formulae. Both actual and fat-free mass body surface areas (BSA) were used when required. Metabolic parameters (blood glucose, insulin, and lipids) were analyzed in the obese subjects. International Diabetes Federation criteria were used to identify metabolic syndrome (MetS).

Results

We did not detect statistically significant differences between the obese and control groups for mean Cr (p=0.658) and mean cystatin C (p=0.126). Mean cystatin C levels of MetS patients were significantly higher than those of non-MetS obese participants (p<0.001). Cr-based GFR measurements, BCM-based measurements and a combined Cr and cystatin C measurement showed a statistically significant increase in the GFR of obese subjects compared to controls (p=0.002 and p<0.001). This increase was negatively correlated with duration of obesity. Estimations based on actual or fat-free mass BSA did not differ either. Only the Filler equation showed a statistically significant decrease in eGFR in MetS patients. There were no statistically significant differences between the obese and control groups for proteinuria (p=0.994) and fat-free mass proteinuria (p=0.476).

Conclusion

We conclude that cystatin C could be used as an earlier biomarker than Cr in the detection of impaired renal function in obese children, especially those with MetS. Cr-based formulae reveal hyperfiltration as the first change in renal function. Decreasing eGFR seen in MetS patients with cystatin C-based formulae, but not Cr-based formulae, may represent the early stages of renal damage. Using fat-free mass or BCM for eGFR formulae in obese children seems to provide no additional information.

Cystatin C in adipose tissue and stimulation of its production by growth hormone and triiodothyronine in 3T3-L1 cells

Cystatin C (CysC) is a marker for estimation of glomerular filtration rate (GFR). CysC levels may depend not only on clearance/GFR but possibly also on changes in production. Our studies on tissue distribution of CysC protein in mice showed that adipose tissue expresses significant amounts of CysC, suggesting that adipocytes could contribute to circulating CysC levels in vivo. As growth hormone (GH) and triiodothyronine (T₃) increase both GFR and CysC (increased in acromegaly and hyperthyroidism) in vivo, we studied whether they could increase CysC production in 3T3-L1 adipocytes in vitro. CysC accumulated in culture media of 3T3-L1 adipocytes in a time-dependent fashion. GH and T₃ both (10 nmol/l) increased accumulation of CysC, to 373 ± 14 and 422 ± 20, respectively, vs 298 ± 10 ng per well over 4 days in controls. Thus, GH and T₃ enhance the production of CysC by adipocytes in vitro.

Pediatric Inflammatory Bowel Diseases: Should We Be Looking for Kidney Abnormalities?

BACKGROUND

Kidney disease has been reported in adults with inflammatory bowel disease (IBD) and is regarded an extraintestinal manifestation or more rarely a side effect of the medical treatment.

METHODS

In this cross-sectional study we describe the extent of kidney pathology in a cohort of 56 children with IBD. Blood and urine samples were analyzed for markers of kidney disease and ultrasonography was performed to evaluate pole-to-pole kidney length.

RESULTS

We found that 25% of the patients had either previously reported kidney disease or ultrasonographic signs of chronic kidney disease. The median kidney size compared with normal children was significantly reduced. In a multivariate linear mixed model, small kidneys significantly correlated with the use of infliximab, whereas the use of enteral nutritional therapy was associated with larger kidneys.

CONCLUSION

Children with IBD are at risk of chronic kidney disease, and the risk seems to be increased with the severity of the disease.

Effect of cardiac rehabilitation on the renal function in chronic kidney disease - Analysis using serum cystatin-C based glomerular filtration rate

Background

Whether an individually determined appropriate level of cardiac rehabilitation (CR) has a favorable effect on the renal function still remains unclarified. The aim of this study was to confirm the effect of CR on the estimated glomerular filtration rate (eGFR) using cystatin C, which is known to be unaffected by physical exercise.

Methods

The study population was comprised of 86 patients (61 males; average age 74 y/o) with a lower-moderate level of chronic kidney disease (CKD) who was admitted to our hospital for treatment of cardiovascular disease (CVD) and who participated in our 3-month CR program. The exercise capacity was assessed by cardiopulmonary exercise testing (CPX) and the eGFR was measured by a formula based on the serum cystatin C concentration (eGFRcys) in each patient both at the beginning and end of the CR.

Results

In the CVD patients with CKD, both the peak oxygen uptake (VO₂) and peak work rate (WR) improved significantly after CR (15.0 ± 3 to 15.8 ± 3 ml/min/kg, p = 0.002. 65.5 ± 21 to 70.2 ± 25 W, p = 0.001). Regarding the renal function, the eGFRcys improved (45.2 ± 11 to 47.3 ± 13 ml/min/1.73 m², p = 0.023), however, the eGFR assessed by the serum creatinine (eGFRcr) did not improve after CR (45.1 ± 12 to 44.9 ± 13 ml/min/1.73 m², p = 0.834).

Conclusions

In CVD patients, a novel CR program significantly improved the exercise capacity. Further, CR was shown to have a favorable effect on the renal function when it was estimated by the eGFRcys.

•

Cardiac rehabilitation improved the renal function using serum cystatin C.

•

Cardiac rehabilitation didn't change the renal function using serum creatinine.

•

Cardiac rehabilitation is most effective on moderate to severe CKD patients.

Effect of socio-demographic factors on endogenous biomarkers (cystatin C and creatinine) among elderly chronic kidney disease patients: a cross-sectional study

PURPOSE

Creatinine is normally used to evaluate kidney function among elderly patients in clinical practice, which has been reported to be affected by socio-demographic factors like BMI and age. Cystatin C a newly introduced biomarker may be more efficient in identifying kidney function in obese and aged CKD patients. The aim of the current study was to assess the effect of BMI on endogenous biomarkers (cystatin C and creatinine) among elderly CKD patients in Malaysia, a first such study in the country.

METHODS

The current study was conducted at the Hospital University Sains Malaysia, Kelantan. A total of 300 elderly Malay participants ≥ 65 years, with CKD, were taken in study. Demographic data, blood pressure, weight, and height were documented. Serum creatinine was assayed by Chemistry Analyzer Model Architect-C8000 (Jaffe Method), while serum cystatin C was examined by Human cystatin C ELISA kit (Sigma-Aldrich) using Thermo Scientific Varioskan Flash ELISA reader.

RESULTS

The study participants were divided into three groups on the basis of age. There was a statistically significant difference at the p value < 0.05 in serum creatinine level for the three age groups [F (2, 297) = 1.98, p value 0.045]. Patients were divided into four groups on the basis of BMI. The results of one-way ANOVA revealed a statistically significant difference at the p value < 0.05 in the mean serum creatinine level for the four groups [F (3, 396) = 2.99, p value 0.032]. However, no statistically significant differences between mean serum cystatin C levels were observed on the basis of patient's age and BMI.

CONCLUSION

Cystatin C is not related to BMI and age among elderly chronic kidney disease patients. The study clearly evaluates the role of serum cystatin C as a good competitor of creatinine among the elderly CKD patients.

Population pharmacokinetics of teicoplanin in hospitalized elderly patients using cystatin C as an indicator of renal function

OBJECTIVE

Serum cystatin C (CysC) has recently been proposed as an alternative marker to serum creatinine (SCR) for estimating renal clearance. In the present study, we performed a population pharmacokinetic analysis of teicoplanin (TEIC), which is mainly eliminated through the kidneys, using CysC as a predictor for renal clearance.

METHODS

Thirty-six patients with MRSA infections who were administrated to the National Hospital Organization Beppu Medical Center between January 2012 and December 2013 were enrolled and gave 123 sets of blood TEIC concentration data. Renal clearance was estimated by the Hoek equation using CysC, by creatinine clearance predicted by the Cockcroft-Gault equation using SCR, or directly by CysC. One compartment open model with inter-individual variabilities for renal clearance and the volume of distribution as well as an additional residual error model was used to estimate population pharmacokinetic parameters for TEIC.

RESULTS

The model with the best predictability was that with CysC as a predictor for renal clearance; it showed better significance than the models using estimated the glomerular filtration rate by the Hoek equation or CLcr. The final model was as follows: CL (L/hr) = 0.510 × (CysC/1.4)^-0.68 × Total body weight/60^0.81, omega (CL) = 19.8% CV, VC (L) = 78.1, omega (V) = 42.7% CV.

CONCLUSION

The present results show the usefulness of CysC to more accurately predict the pharmacokinetics of drugs mainly eliminated through the kidneys, such as TEIC. However, since the sample size in this study was relatively small, further investigations on renal clearance predictability using CysC are needed.

Inverse Relationship between Adherence to the Mediterranean Diet and Serum Cystatin C Levels

OBJECTIVE

The aim of the present study was to examine serum cystatin C levels in association with the Mediterranean diet in a healthy Greek population.

METHODS

Cystatin C together with basic clinical chemistry tests was measured in a total of 490 adults (46±16 years, 40% of males), who underwent an annual health check. Demographic, anthropometric and lifestyle characteristics were recorded, while adherence to the Mediterranean diet was evaluated through the MedDietScore (0-55).

RESULTS

The mean level of serum cystatin C was 0.84 mg/L, while men had increased serum cystatin C levels compared to women (0.86 mg/L vs. 0.83 mg/L, respectively, 0.017). After adjusting for age, gender, body mass index, smoking status, hypertension, diabetes, hypercholesterolemia, estimated glomerular filtration rate (eGFR), albumin and ferritin levels, each unit increase in MedDietScore led to 0.002 mg/dL drop off in cystatin C serum levels.

CONCLUSIONS

We have demonstrated an inverse relationship between the MedDietScore and serum cystatin C levels. Our finding that increases in MedDietScore are associated with decreases in serum cystatin C levels could imply that adherence to the Mediterranean diet may reduce the cardiovascular risk, as assessed by cystatin C, a prognostic marker of the cardiometabolic risk. This notion could have a great impact on public health.

Adult Reference Ranges for Serum Cystatin C, Creatinine and Predicted Creatinine Clearance

Serum cystatin C measurement has been previously shown by ourselves and others to be a better indicator of changes in glomerular filtration rate (GFR) than serum creatinine. However, the available literature on reference values for cystatin C concentration remains surprisingly sparse; we thus set out to determine an adult reference range. Blood was taken from 309 healthy blood donors and creatinine and cystatin C concentrations were measured using commercially available automated methodologies. In addition, predicted creatinine clearances were calculated using the Cockcroft and Gault formula. The 95% reference intervals for creatinine, predicted creatinine clearance and cystatin C for all blood donors, regardless of gender, were 68–118 μmol/L, 58–120 ml/min/1·73 m2 and 0·51–0·98 mg/L, respectively. For women, the intervals were 68–98 μmol/L, 60–119 ml/min/1·73 m2 and 0·49–0·94 mg/L; for men, they were 78–123 μmol/L, 57–122 ml/min/1·73 m2 and 0·56–0·98 mg/L. The mean 95% reference interval for cystatin C in all donors under 50 years of age was 0·53–0·92 mg/L; for those over 50 years of age it was 0·58–1·02 mg/L. The small difference between male and female ranges meant that a single reference range for cystatin C could be established for all adults under 50 years of age without adjustment for body surface area. Serum cystatin C measurement offers a simpler and more sensitive screening test than serum creatinine for early changes in GFR.

Effects of Oral Prednisone Administration on Serum Cystatin C in Dogs

Background

Oral administration of glucocorticoid alters serum cystatin C (sCysC) concentration in humans.

Objective

To determine if oral administration of prednisone alters sCysC in dogs without pre‐existing renal disease.

Animals

Forty six dogs were included: 10 dogs diagnosed with steroid responsive meningitis arteritis (SRMA; group A), 20 dogs diagnosed of pituitary‐dependent hyperadrenocorticism (PDH; group B), and 16 healthy control dogs (group C).

Methods

Retrospective observational study. SRMA diagnosed dogs were administered prednisone 4 mg/kg/24 h PO 7 days, reducing the dose to 2 mg/kg/24 h 7 days before medication withdrawal. In group A, sampling was performed at days 0, 7, 14 and a final control at day 21. Blood and urine samples were collected in the 3 groups, and in group A, sampling was performed at all time points (days 1, 7, 14, and 21).

Results

In group A, sCysC was significantly higher at day 7 compared to the control group (0.4 ± 0.04 mg/L vs. 0.18 ± 0.03 mg/L mean ± SEM respectively P < 0.01); sCysC values decreased to basal at day 14 when the dose was decreased and after 1 week of withdrawal of prednisone (0.27 ± 0.03 mg/L for group A at day 14 and 0.15 ± 0.02 mg/L at day 21; P > 0.05). Dogs with PDH included in group B did not have significant differences in sCysC (0.22 ± 0.03 mg/L) compared to control (P > 0.05).

Conclusions and Clinical Importance

Oral administration of prednisone unlike altered endogenous glucocorticoid production, increases sCysC in dogs in a dose‐dependent fashion.

Journey of cystatins from being mere thiol protease inhibitors to at heart of many pathological conditions

Cystatins are thiol proteinase inhibitors (TPI), present ubiquitously in animals, plants and micro-organisms. These are not merely inhibitors rather they are at heart of many pathological conditions ranging from diabetes to renal failure. These are essential for maintenance of protein balance of the cell; once this balance gets disturbed, it may lead to cell death. Thus, cystatins cannot be merely regarded as TPI's as these have been found to play a pivotal role in tumorigenesis and neurodegenerative diseases. Many studies have reported the variation in cystatin level in incidences of different types of cancer; highlighting an important role played by these inhibitors in cancer development and progression. Cystatin C is increasingly replacing creatinine as a biomarker of glomerular filtration rate (GFR) thereby highlighting the importance of this important inhibitor. Some recent studies have also reported the interaction pattern of various anti-cancer drugs with cystatins in a bid to find how these drugs affect this important inhibitors and whether these drugs have any side effect on cystatins. Thus, in this growing disease era it can be said that cystatins are no more just inhibitors blocking the activity of thiol proteases rather they play a pivotal role in variety of pathological conditions.

The Relationship between Renal Function and Bone Marrow Density in Healthy Korean Women

OBJECTIVES

The relationship between renal function and bone mineral density (BMD) is controversial. We evaluated the relationship between markers of renal function and BMD in healthy Korean women.

METHODS

A total of 1,093 women who visited the health promotion center at Pusan National University hospital were included in the cross-sectional study. We divided the study population into two groups by BMD: osteopenia-osteoporosis and normal in the lumbar and femur regions, respectively. We compared the relationship between renal function and BMD using a logistic regression model and used SAS 9.3 (SAS Institute, Inc., Cary, NC, USA) for all statistical analysis.

RESULTS

Blood urea nitrogen (BUN), creatinine, and cystatin C (Cys-C) were correlated with BMD in both the normal and osteopenia-osteoporosis groups, and in logistic regression analysis, BUN and Cys-C were correlated with lumbar and femur BMD. However, after we adjusted for age, menopause, and body mass index, only creatinine showed a negative correlation with lumbar BMD, and estimated glomerular filtration rate (eGFR) was related positively with femur BMD.

CONCLUSIONS

Serum creatinine could be a marker for lumbar BMD and eGFR for femur BMD in Korean women without overt nephropathy.