Urinary cystatin C as an early biomarker of acute kidney injury following adult cardiothoracic surgery

Urinary and Plasma miRNAs in the Early Detection of Acute Kidney Injury and Their Possible Role as Therapeutic Targets

Acute Kidney Injury (AKI) is a severe clinical condition featured by a rapid decrease in kidney function in a short period of time. AKI, which is often secondary to sepsis, ischemia-reperfusion and drug toxicity, is associated to high morbidity and mortality. Moreover, it contributes to the development of chronic kidney disease (CKD), due to maladaptive or incomplete repair mechanisms, resulting in renal fibrosis. Small non-coding RNA has recently emerged as a novel biomarker for the early detection and treatment of AKI. In particular, microRNAs (miRNAs) are non-coding RNA molecules of 21-25 nucleotides regulating the expression of protein-coding genes through sequence-specific recognition. Due to their high stability in biological fluids, such as urine and plasma, they can be reliably analyzed and quantified, and for this reason they can be considered potential diagnostic and therapeutic biomarkers. Specifically, miRNAs have been demonstrated to predict AKI before the increase in creatinine levels, thus improving the management of this syndrome. In this review, we provide a comprehensive overview of the role of urinary and plasma miRNAs in the early detection and treatment of AKI.

The efficacy of novel biomarkers for the early detection and management of acute kidney injury: A systematic review

Acute kidney injury (AKI) is a frequent clinical complication lacking early diagnostic tests and effective treatments. Novel biomarkers have shown promise for enabling earlier detection, risk stratification, and guiding management of AKI. We conducted a systematic review to synthesize evidence on the efficacy of novel biomarkers for AKI detection and management. Database searches yielded 17 relevant studies which were critically appraised. Key themes were biomarker efficacy in predicting AKI risk and severity before functional changes; potential to improve clinical management through earlier diagnosis, prognostic enrichment, and guiding interventions; emerging roles as therapeutic targets and prognostic tools; and ongoing challenges requiring further validation. Overall, novel biomarkers like neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule-1 (KIM-1), and cell cycle arrest markers ([TIMP-2] •[IGFBP7]) demonstrate capability for very early AKI prediction and accurate risk stratification. Their incorporation has potential to facilitate timely targeted interventions and personalized management. However, factors influencing biomarker performance, optimal cutoffs, cost-effectiveness, and impact on patient outcomes require robust validation across diverse settings before widespread implementation. Addressing these limitations through ongoing research can help translate novel biomarkers into improved detection, prognosis, and management of AKI in clinical practice.

Kidney Injury under Diminished Pulsatile Flow Induced by V-A ECMO in Sheep

Extracorporeal membrane oxygenation (ECMO) is commonly used for critically ill patients and associated with high rates of kidney injury and mortality. This study aimed to assess the impact of diminished pulsatile flow induced by veno-arterial ECMO (V-A ECMO) on kidney structure and function. Ten healthy sheep were divided into two groups (n=5 each) to compare diminished pulsatile flow induced by V-A ECMO with normal pulsatile flow under veno-venous ECMO (V-V ECMO) over 7 days. Vital signs were recorded every 6 hours, and renal biomarkers were tested every 24 hours. The pulse pressure (PP) in the V-A ECMO group was around 20 mmHg, compared to 30 mmHg in the V-V ECMO group. The pulsatility index (PI) was lower than 0.25 in the V-A ECMO group and higher in the V-V ECMO group. Mixed model results showed significant differences in PP and PI between the two groups (p = 0.044 and p = 0.016, respectively). BUN and Cr levels were similar in both groups, but Cystatin C was higher in the diminished pulsatile flow group. The expression of anti-platelet endothelial cell adhesion molecule-1 (CD31) and the renin-positive glomerulus ratio were significantly lower in the diminished pulsatile flow group. Both groups exhibited hypoxia-inducible factor-1α (HIF-1α) in renal tubules, indicating hypoxia. These findings suggest diminished pulsatile flow under V-A ECMO affects renal endothelial cell proteins and renin secretion. During the management of ECMO, although the serum BUN and Cr were normal, there was exactly an early-stage injury of the glomerulus and tubules in both groups.

The value of serum cystatin c in predicting acute kidney injury after cardiac surgery: A systematic review and meta-analysis

OBJECTIVE

This study aims to review relevant research and assess the diagnostic value of serum cystatin C (CysC) for post-cardiac surgery acute kidney injury (PCSAKI).

METHOD

We searched databases (PubMed, Embase, Cochrane, WanFang, CNKI, VIP) for literature published up to January 10, 2024. Quality was assessed using Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2). Extracted data from eligible studies and summarized sensitivity, specificity, and area under the curve (AUC) values.

RESULTS

A total of 24 studies involving 3,427 patients were included. The estimated diagnostic sensitivity of CysC for PCSAKI was 0.67 (95% CI, 0.57-0.76), with a specificity of 0.87 (95% CI, 0.81-0.91). The positive likelihood ratio (+LR) was 5.17 (95% CI, 3.45-7.73), and the negative likelihood ratio (-LR) was 0.38 (95% CI, 0.28-0.51). The diagnostic odds ratio (DOR) was 14 (95% CI, 7-26), the diagnostic score (DS) was 2.62 (95% CI, 1.99-3.24), and AUC was 0.86 (95% CI, 0.83-0.89). The sub-analysis results indicate that gender distribution, serum storage temperature, CysC detection method, and detection time all have a significant impact on sensitivity and specificity.

CONCLUSION

CysC has high specificity and good sensitivity in diagnosing PCSAKI during the perioperative period, with better detection results 24 hours before surgery, making it suitable for early detection. However, whether and how CysC is commonly used in clinical diagnosis still requires further research and clinical trials.

FRET-Based Dual-Color Carbon Dot Ratiometric Fluorescent Sensor Enables the Smartphone-Integrated Device for Noninvasive and Portable Diagnosis of Chronic Kidney Disease

Cystatin C (Cys C), a crucial renal disease marker for chronic kidney disease (CKD), plays a vital role in early diagnosis and treatment guidance. However, most current methods for detecting Cys C rely on a single signal and find it difficult to perform noninvasive and portable diagnosis. Here, we developed a ratiometric fluorescent carbon dot (CD) detection system for point-of-care testing (POCT) of Cys C through fluorescence resonance energy transfer (FRET). The detection is based on the hydrolysis effect of papain on a bovine serum albumin (BSA) scaffold and the specific inhibitory effect of Cys C on papain, endowing high-resolution color variance. Moreover, a low-cost, portable, yet reliable smartphone-assisted miniaturized device for real-time quantitative POCT of Cys C has been developed with a limit of detection (LOD) as low as 0.4 μg/mL. This sensing platform can effectively differentiate patients from healthy volunteers, which facilitates self-screening for healthy individuals and home monitoring for CKD patients.

Long wavelength light exposure reduces systemic inflammation coagulopathy and acute organ injury following multiple injuries in mice

BACKGROUND

Evidence suggests that variation in light exposure strongly influences the dynamic of inflammation, coagulation, and the immune system. Multiple injuries induce systemic inflammation that can lead to end-organ injury. Here, we hypothesize that alterations in light exposure influence posttrauma inflammation, coagulopathy, and end-organ injury.

METHODS

C57BL/6 mice underwent a validated multiple-injury and hemorrhage model performed following 72 hours of exposure to red (617 nm, 1,700 lux), blue (321 nm, 1,700 lux), and fluorescent white light (300 lux) (n = 6-8/group). The animals were sacrificed at 6 hours posttrauma. Plasma samples were evaluated and compared for proinflammatory cytokine expression levels, coagulation parameters, markers of liver and renal injury, and histological changes (Carstairs staining). One-way analysis of variance statistical tests were applied to compare study groups.

RESULTS

Preexposure to long-wavelength red light significantly reduced the inflammatory response at 6 hours after multiple injuries compared with blue and ambient light, as evidenced by decreased levels of interleukin 6, monocyte chemoattractant protein-1 (both p < 0.001), liver injury markers (alanine transaminase, p < 0.05), and kidney injury markers (cystatin C, p < 0.01). In addition, Carstairs staining of organ tissues revealed milder histological changes in the red light-exposed group, indicating reduced end-organ damage. Furthermore, prothrombin time was significantly lower ( p < 0.001), and fibrinogen levels were better maintained ( p < 0.01) in the red light-exposed mice compared with those exposed to blue and ambient light.

CONCLUSION

Prophylactic light exposure can be optimized to reduce systemic inflammation and coagulopathy and minimize acute organ injury following multiple injuries. Understanding the mechanisms by which light exposure attenuates inflammation may provide a novel strategy to reducing trauma-related morbidity.

Cardiac Surgery-Associated Acute Kidney Injury

AKI is a common and serious complication of cardiac surgery that has a significant impact on patient morbidity and mortality. The Kidney Disease Improving Global Outcomes definition of AKI is widely used to classify and identify AKI associated with cardiac surgery (cardiac surgery-associated AKI [CSA-AKI]) on the basis of changes in serum creatinine and/or urine output. There are various preoperative, intraoperative, and postoperative risk factors for the development of CSA-AKI which should be recognized and addressed as early as possible to expedite its diagnosis, reduce its occurrence, and prevent or ameliorate its devastating complications. Crucial issues are the inaccuracy of serum creatinine as a surrogate parameter of kidney function in the perioperative setting of cardiothoracic surgery and the necessity to discover more representative markers of the pathophysiology of AKI. However, except for the tissue inhibitor of metalloproteinase-2 and insulin-like growth factor binding protein 7 ratio, other diagnostic biomarkers with an acceptable sensitivity and specificity are still lacking. This article provides a comprehensive review of various aspects of CSA-AKI, including pathogenesis, risk factors, diagnosis, biomarkers, classification, prevention, and treatment management.

Evaluation of renal function in precarious workers exposed to heavy metals in vulnerable scenarios in the metropolitan area of San Luis Potosí, México

The aim of the study was to evaluate renal function in three groups of precarious workers: garbage recyclers (REC), quarry workers (CAN), and brick makers (LAD). Samples of urine and blood were collected to evaluate clinical parameters and the metal levels in urine was measured using ICP-MS. REC group had the highest concentrations of chromium in urine (36.03 ± 27.2 µg/l) compared to CAN and LAD groups. Mercury concentrations were higher in the LAD group (3.7 ± 0.8 µg/l). Additionally, arsenic was detected in both CAN and REC groups (25.4 ± 26.2 and 19.09 ± 16.7 µg/l, respectively), while arsenic concentrations in LAD were higher (47.2 ± 30.8 µg/l). In kidney biomarkers, β2-microglobulin concentrations were higher in the REC group (87867 ± 115159.5 ng/g UCr). Similarly, cystatin-C concentrations were higher in the REC group (32795.61 ± 34965.8 ng/g UCr). The data suggests that precarious workers are exposed to heavy metals and have elevated protein levels that contribute to kidney damage.

Fluoride exposure and pediatric kidney health in dry, wet and intermediate climatic zone communities in Sri Lanka: Implications from urinary Cystatin-C, and albumin-creatinine ratio

BACKGROUND

High fluoride exposure is increasingly discussed attributing to kidney injury as a causative factor. Depending on geochemistry, differential fluoride levels in drinking water are identified in different regions in Sri Lanka. However, the levels of fluoride exposure, and associations with kidney health has not been adequately studied in Sri Lanka, particularly in pediatric communities. Hence, the present study aimed to assess fluoride exposure in selected pediatric communities in the dry, wet and intermediate climatic zones in Sri Lanka, along with an assessment of renal health using urinary Cystatin-C (uCys-C), and albumin-creatinine ratio (uACR).

METHODS

We conducted a cross-sectional study with school students in selected education zones representing dry (N = 331), wet (N = 152), and intermediate (N = 292) climatic zones in Sri Lanka. Fluoride contents in urine and drinking water were assessed as measures of fluoride exposure.

RESULTS

The median (interquartile distance) urinary fluoride levels of participants in the dry, wet and intermediate zones were 1.63(1.04-2.85), 1.29(0.85-2.21), and 1.07(0.61-1.98) mg/gCr while the fluoride contents of drinking water samples were 1.76(1.36-2.30), 0.25(0.18-0.37), and 0.43(0.26-0.63) ppm respectively with significant differences among the three groups. Median uCys-C level (ng/mgCr) of the participants in intermediate zone [30.26(8.49-71.44)] was significantly low (p < 0.05) compared to that of the participants in dry zone [56.19(7.08-211.8)], and wet zone [66.29(30.43-125.20)]. The incidences of elevated uCys-C levels above reference intervals in participants of dry zone (47.7%), and wet zone (50.0%) were significantly high (p < 0.001) compared to the intermediate zone (26.4%).

CONCLUSION

Relatively high fluoride exposure is likely in dry and wet zone communities compared to the intermediate zone along with significantly higher incidence of uCys-C levels above reference intervals in study groups with higher fluoride exposure. However, to conclude a clear link between fluoride exposure and kidney health we need in-depth studies.

Global biomarkers trends in acute kidney injury: a bibliometric analysis

OBJECTIVES

Acute kidney injury (AKI) is a common global condition with high morbidity and mortality rates. Biomarkers can aid in the diagnosis, prediction, intervention, and outcome assessment of AKI. This study aimed to summarize the current research status and identify research hotspots for AKI biomarkers using bibliometric analysis.

METHODS

Relevant original English language articles were retrieved from the Science Citation Index Expanded of the Web of Science Core Collection database, from inception to 31 December 2022. Full records and related cited references from all the documents were collected and analyzed.

RESULTS

A total of 16368 authors from 3379 institutions in 83 countries/regions contributed to 2916 documents that were published in 712 academic journals. Annual publication output followed exponential growth since 2008. The United States, the University of Pittsburgh, and the American Journal of Physiology-Renal Physiology were the most productive countries, institutions, and journals in terms of research outputs, respectively. The area of interest has shifted from neutrophil gelatinase-associated lipocalin, cell cycle, and tubular damage toward sepsis and COVID-19. Apoptosis, inflammation, and chronic kidney disease have become popular in recent years, and studies on ferroptosis, machine learning, COVID-19, and renal fibrosis will be the focus of future research.

IMPLICATIONS

This bibliometric study suggests that future research on AKI biomarkers would focus on ferroptosis, renal fibrosis and COVID-19. Artificial intelligence, such as machine learning, maybe the most promising direction for the discovery and validation of AKI biomarkers.

The Urinary Concentrations of Neutrophil Gelatinase-Associated Lipocalin, Cystatin C and Osteopontin in the Healthy Term and Stable Preterm Neonates: A Pilot Study

BACKGROUND

In neonates, the assessment of kidney function with serum creatinine is limited; therefore, more effective biomarkers are needed.

AIM

The study aimed at analyzing the concentrations of renal biomarkers (osteopontin, cystatin C, and NGAL) in neonates.

MATERIAL AND METHODS

The study included 80 term and 20 preterm neonates aged 28-33 weeks of gestation. Biomarkers were measured in urine. Term neonates' urine was collected on the 1st day of life. Preterm neonates' urine was collected on the 1st, 8th, 15th, 22nd day of life. Biomarkers' concentrations were normalized to urinary creatinine (cr.) and presented as urinary biomarker/cr. ratios.

RESULTS

Median values of biomarker/creatine ratios in term and preterm neonates were the following: cystatin C/cr.: 7.26 and 439.49; osteopontin/cr.: 135.86 and 1633.37; NGAL/cr. in girls: 212.14 and 256.93; and NGAL/cr. in boys 27.123 and 65.29 ng/mg cr. In preterm neonates the cystatin C/cr. ratio was higher on the 1st than on the 8th day. The osteopontin/cr. ratio did not differ between the days. The NGAL/cr. ratio in girls was higher on the 8th than on the 22nd day, and in boys, the lowest was on the 22nd day.

CONCLUSIONS

Prematurity in stable, Caucasian neonates might cause higher osteopontin and cystatin C excretion, but not NGAL. The excretion of NGAL and cystatin C, but not osteopontin, may change during first weeks of premature neonate's life.

Comparing diagnostic accuracy of biomarkers for acute kidney injury after major surgery: A PRISMA systematic review and network meta-analysis

BACKGROUND

The timely identification of patients at risk of acute kidney injury (AKI), along with early prevention, real-time monitoring, and prompt intervention, plays a crucial role in enhancing patient prognosis after major surgery.

METHODS

We conducted a comprehensive search across multiple databases, including Web of Science, EMBASE, MEDLINE, China National Knowledge Infrastructure, and Cochrane Library. Each study's risk of bias was independently evaluated as low, moderate, or high, utilizing criteria adapted from Quality Assessment of Diagnostic Accuracy Studies 2. The analysis was performed using STATA V.17.0 and R software V.3.4.1. Diagnostic tests were ranked based on the dominance index. We performed meta-analyses to calculate odds ratios (ORs) and 95% confidence intervals (CIs) individually. We then carried out a network meta-analysis to compare the performances of these biomarkers.

RESULTS

Fifteen studies were included in this analysis. The meta-analysis findings revealed that among all the biomarkers assessed, serum cystatin C (s-CysC) (hierarchical summary receiver operating characteristic curve [HSROC] 82%, 95% CI 0.78-0.85) exhibited the highest HSROC value. The network meta-analysis demonstrated that urinary kidney injury molecule-1 (u-KIM-1) and s-CysC displayed relatively higher sensitivity and specificity, respectively. In subgroup analyses, u-KIM-1 in the urine output (OU) group (OR 303.75, 95% CI 3.39-1844.88), s-CysC in the non-OU group (OR 10.31, 95% CI 3.09-26.2), interleukin-18 in the noncardiac surgery group (OR 46.20, 95% CI 0.48-307.68), s-CysC in the cardiac group (OR 12.42, 95% CI 2.9-35.86), u-KIM-1 in the retrospective group (OR 243.00, 95% CI 1.73-1582.11), and s-CysC in the prospective group (OR 8.35, 95% CI 2.34-21.15) had the best diagnostic accuracy. However, it is important to note that existing publication bias may reduce the reliability of the above-mentioned results.

CONCLUSION

The biomarker of s-CysC has the highest HSROC value to predicting acute kidney injury after major surgery in meta-analysis and relatively higher specificity in network meta-analyses. u-KIM-1 exhibited relatively higher sensitivity, with best diagnostic accuracy in the OU and retrospective group in the subgroup analysis.

Ambient black carbon reaches the kidneys

BACKGROUND

Ultrafine particles, including black carbon (BC), can reach the systemic circulation and therefore may distribute to distant organs upon inhalation. The kidneys may be particularly vulnerable to the adverse effects of BC exposure due to their filtration function.

OBJECTIVES

We hypothesized that BC particles reach the kidneys via the systemic circulation, where the particles may reside in structural components of kidney tissue and impair kidney function.

METHODS

In kidney biopsies from 25 transplant patients, we visualized BC particles using white light generation under femtosecond-pulsed illumination. The presence of urinary kidney injury molecule-1 (KIM-1) and cystatin c (CysC) were evaluated with ELISA. We assessed the association between internal and external exposure matrices and urinary biomarkers using Pearson correlation and linear regression models.

RESULTS

BC particles could be identified in all biopsy samples with a geometric mean (5th, 95th percentile) of 1.80 × 103 (3.65 × 102, 7.50 × 103) particles/mm3 kidney tissue, predominantly observed in the interstitium (100 %) and tubules (80 %), followed by the blood vessels and capillaries (40 %), and the glomerulus (24 %). Independent from covariates and potential confounders, we found that each 10 % higher tissue BC load resulted in 8.24 % (p = 0.03) higher urinary KIM-1. In addition, residential proximity to a major road was inversely associated with urinary CysC (+10 % distance: -4.68 %; p = 0.01) and KIM-1 (+10 % distance: -3.99 %; p < 0.01). Other urinary biomarkers, e.g., the estimated glomerular filtration rate or creatinine clearance showed no significant associations.

DISCUSSION AND CONCLUSION

Our findings that BC particles accumulate near different structural components of the kidney represent a potential mechanism explaining the detrimental effects of particle air pollution exposure on kidney function. Furthermore, urinary KIM-1 and CysC show potential as air pollution-induced kidney injury biomarkers for taking a first step in addressing the adverse effects BC might exert on kidney function.

Using Serum Cystatin C to Predict Acute Kidney Injury Following Infant Cardiac Surgery

Acute kidney injury (AKI) following cardiopulmonary bypass (CPB) is associated with increased morbidity and mortality. Serum Cystatin C (CysC) is a novel biomarker synthesized by all nucleated cells that may act as an early indicator of AKI following infant CPB. Prospective observational study of infants (< 1 year) requiring CPB during cardiac surgery. CysC was measured at baseline and 12, 24, 48, and 72 h following CPB initiation. Each post-op percent difference in CysC (e.g. %CysC12h) from baseline was calculated. Clinical variables along with urine output (UOP) and serum creatinine (SCr) were followed. Subjects were divided into two groups: AKI and non-AKI based upon the Kidney Disease Improving Global Outcomes (KDIGO) classification. AKI occurred in 41.9% (18) of the 43 infants enrolled. Patient demographics and baseline CysC levels were similar between groups. CysC levels were 0.97 ± 0.28 mg/L over the study period, and directly correlated with SCr (R = 0.71, p < 0.0001). Although absolute CysC levels were not significant between groups, the %CysC12h was significantly greater in the AKI group (AKI: - 16% ± 22% vs. Non-AKI - 28% ± 9% mg/L; p = 0.003). However, multivariate analysis demonstrated that a lower UOP (Odds Ratio:0.298; 95% CI 0.073, 0.850; p = 0.02) but not %CysC12h was independently associated with AKI. Despite a significant difference in the %CysC12h, only UOP was independently associated with AKI. Larger studies of a more homogenous population are needed to understand these results and to explore the variability in this biomarker seen across institutions.

Increased numbers of pre-operative circulating monocytes predict risk of developing cardiac surgery-associated acute kidney injury in conditions requiring cardio pulmonary bypass

BACKGROUND

Evaluating patients' risk for acute kidney injury (AKI) is crucial for positive outcomes following cardiac surgery. Our aims were first to select candidate risk factors from pre- or intra-operative real-world parameters collected from routine medical care and then evaluate potential associations between those parameters and risk of onset of post-operative cardiac surgery-associated AKI (CSA-AKI).

METHOD

We conducted two cohort studies in Japan. The first was a single-center prospective cohort study (n = 145) to assess potential association between 115 clinical parameters collected from routine medical care and CSA-AKI (≥ Stage1) risk in the population of patients undergoing cardiac surgery involving cardiopulmonary bypass (CPB). To select candidate risk factors, we employed random forest analysis and applied survival analyses to evaluate association strength. In a second retrospective cohort study, we targeted patients undergoing cardiac surgery with CPB (n = 619) and evaluated potential positive associations between CSA-AKI incidence and risk factors suggested by the first cohort study.

RESULTS

Variable selection analysis revealed that parameters in clinical categories such as circulating inflammatory cells, CPB-related parameters, ventilation, or aging were potential CSA-AKI risk factors. Survival analyses revealed that increased counts of pre-operative circulating monocytes and neutrophils were associated with CSA-AKI incidence. Finally, in the second cohort study, we found that increased pre-operative circulating monocyte counts were associated with increased CSA-AKI incidence.

CONCLUSIONS

Circulating monocyte counts in the pre-operative state are associated with increased risk of CSA-AKI development. This finding may be useful in stratifying patients for risk of developing CSA-AKI in routine clinical practice.

The outcome of acute kidney injury substages based on urinary cystatin C in critically ill children

BACKGROUND

The concept of acute kidney injury (AKI) substages has been recommended to better phenotype AKI and identify high-risk patient groups and therefore improve the diagnostic accuracy of AKI. However, there remains a gap between the recommendation and the clinical application. The study aimed to explore the incidence of AKI substages based on a sensitive AKI biomarker of urinary cystatin C (uCysC), and to determine whether AKI substages were relevant with respect to outcome in critically ill children.

RESULTS

The multicenter cohort study enrolled 793 children in pediatric intensive care unit (PICU) of four tertiary hospitals in China. Children were classified as non-AKI, sub-AKI and AKI substages A and B according to uCysC level at PICU admission. Sub-AKI was defined by admission uCysC level ≥ 1.26 mg/g uCr in children not meeting the KDIGO criteria of AKI. In children who fulfilled KDIGO criteria, those with uCysC < 1.26 was defined as AKI substage A, and with ≥ 1.26 defined as AKI substage B. The associations of AKI substages with 30-day PICU mortality were assessed. 15.6% (124/793) of patients met the definition of sub-AKI. Of 180 (22.7%) patients with AKI, 90 (50%) had uCysC-positive AKI substage B and were more likely to have classical AKI stage 3, compared to substage A. Compared to non-AKI, sub-AKI and AKI substages A and B were risk factors significantly associated with mortality, and the association of sub-AKI (adjusted hazard ratio HR = 2.42) and AKI substage B (adjusted HR = 2.83) with mortality remained significant after adjustment for confounders. Moreover, AKI substage B had increased risks of death as compared with sub-AKI (HR = 3.10) and AKI substage A (HR = 3.19).

CONCLUSIONS

Sub-AKI defined/based on uCysC occurred in 20.2% of patients without AKI and was associated with a risk of death close to patients with AKI substage A. Urinary CysC-positive AKI substage B occurred in 50% of AKI patients and was more likely to have classical AKI stage 3 and was associated with the highest risk of mortality.

Role of serum cystatin C in the prediction of acute kidney injury following pediatric cardiac surgeries: A single center experience

Intense contemporary research is directed towards validating novel biomarkers to predict acute kidney injury (AKI) in children undergoing cardiothoracic surgeries. We aimed to evaluate the role of cystatin C in early prediction of AKI following cardiac surgery in children with congenital heart disease. Prospective observational cohort study was conducted on 40 children with congenital heart disease undergoing cardiac surgery. 40 healthy children with matched age and sex were enrolled as a control group. Children were subjected to physical examination, routine blood tests, echocardiography, and measurement of plasma cystatin C level on different occasions. The median age of the patients was 3.65 years, a range from 1 to 5 years with no significant difference regarding the age and sex of cases and control groups. The mean serum cystatin C level in patients was 0.75 ± 0.15, 1.35 ± 0.34 and 1.21 ± 0.38 mg/dL (preoperative, at 6 h and at 24 h postoperative, respectively) with statistically significant difference P < .05. 30% of the patients developed postoperative AKI with significantly higher serum cystatin C at 6 hours postoperative >1.33 mg/dL compared to preoperative level p P < .05. Serum cystatin C level was positively correlated with cardiac bypass time, ischemic time and length of hospital stay at 6 hours postoperative. Serum cystatin C is a sensitive marker for early detection of AKI following cardiac surgery in children with congenital heart disease and it was positively correlated with cardiac bypass time, ischemic time and length of hospital stay.

Serum Cystatin C Levels Could Predict Rapid Kidney Function Decline in A Community-Based Population

BACKGROUND

Several biomarkers have been correlated with the prevalence and severity of chronic kidney disease (CKD); however, the association between biomarkers and rapid kidney function decline (RKFD) is unknown. This study aimed to evaluate the predictive performance of biomarkers to determine who is likely to develop RKFD in a healthy population.

METHODS

A community-based cohort of 2608 people residing in northern Taiwan were enrolled, and their renal function was followed annually from January 2014 to December 2019. The outcomes of interest were RKFD, defined as a 15% decrease in the estimated glomerular filtration rate (eGFR) within the first 4 years, and a decrease in eGFR without improvement in the fifth year. Clinical variables and potential predictors of RKFD, namely adiponectin, leptin, tumor necrosis factor-alpha, and cystatin C, were measured and analyzed.

RESULTS

The incidence of RKFD was 17.0% (105/619). After matching for age and sex at a 1:1 ratio, a total of 200 subjects were included for analysis. The levels of cystatin C and total vitamin D were significantly negatively correlated with eGFR. eGFR was negatively correlated with the levels of cystatin C and total vitamin D. Among the biomarkers, cystatin C showed the best predictive performance for RKFD (area under the receiver operating characteristic curve: 0.789). Lower serum cystatin C was associated with a higher rate of RKFD in healthy subjects. A generalized additive model showed that 0.82 mg/L was an adequate cut-off value of cystatin C to predict RKFD. Multivariable logistic regression analysis further indicated that low cystatin C and eGFR were independent predictors of the possibility of RKFD.

CONCLUSIONS

Serum cystatin C level could predict the possibility of RKFD. We suggest that a low cystatin C level should be considered as a risk factor for RKFD in healthy subjects.

Mobilization of CD11b+/Ly6chi monocytes causes multi organ dysfunction syndrome in acute pancreatitis

Objective

Acute pancreatitis (AP) is an inflammatory disorder, the severe form of which is burdened with multi-organ dysfunction and high mortality. The pathogenesis of life –threatening organ complications, such as respiratory and renal failure, is unknown.

Design

Organ dysfunction was investigated in a mouse model of AP. The influence of monocytes and neutrophils on multi organ dysfunction syndrome (MODS) was investigated in vivo by antibody depletion. Using real-time-fluorescence and deformability-cytometry (RT-DC) analysis we determined the mechanical properties of neutrophils and monocytes during AP. Furthermore, blood samples of pancreatitis patients were used to characterize severity-dependent chemokine profiles according to the revised Atlanta classification.

Results

Similar to AP in humans, severe disease in the mouse model associates with organ dysfunction mainly of lung and kidney, which is triggered by a mobilisation of Ly6g^-/CD11b⁺/Ly6c ^hi monocytes, but not of Ly6g⁺/CD11b⁺ neutrophils. Monocyte depletion by anti-CCR2 antibody treatment ameliorated lung function (oxygen consumption) without interfering with the systemic immune response. RT-DC analysis of circulation monocytes showed a significant increase in cell size during SAP, but without a compensatory increase in elasticity. Patient chemokine profiles show a correlation of AP severity with monocyte attracting chemokines like MCP-1 or MIG and with leukocyte mobilisation.

Conclusion

In AP, the physical properties of mobilized monocytes, especially their large size, result in an obstruction of the fine capillary systems of the lung and of the kidney glomeruli. A selective depletion of monocytes may represent a treatment strategy for pancreatitis as well as for other inflammation-related disorders.

Improving acute kidney injury diagnostic precision using biomarkers

Acute kidney injury (AKI) is common in hospitalized patients of all ages and is associated with significant morbidity and mortality. Accurate prediction and early identification of AKI is of utmost importance because no therapy exists to mitigate AKI once it has occurred. Yet, serum creatinine lacks adequate sensitivity and specificity, and quantification of urine output is challenging in incontinent children without indwelling bladder catheters. Integration of clinically available biomarkers have the potential to delineate unique AKI phenotypes that could have important prognostic and therapeutic implications. Plasma Cystatin C, urine neutrophil gelatinase associated lipocalin (NGAL) and the urinary product of tissue inhibitor metalloproteinase (TIMP-2) and insulin growth factor binding protein-7 (IGFBP7) are clinically available. These biomarkers have been studied in heterogenous populations across the age spectrum and in a variety of clinical settings for prediction of AKI. The purpose of this review is to describe and discuss the clinically available AKI biomarkers including how they have been used to delineate AKI phenotypes.

Biomarkers of acute kidney injury in pediatric cardiac surgery

Acute kidney injury (AKI) is characterized by a sudden decrease in kidney function. Children with congenital heart disease are a special group at risk of developing AKI. We performed a systematic review of the literature to search for studies reporting the usefulness of novel urine, serum, and plasma biomarkers in the diagnosis and progression of AKI and their association with clinical outcomes in children undergoing pediatric cardiac surgery. In thirty studies, we analyzed the capacity to predict AKI and poor outcomes of five biomarkers: Cystatin C, Neutrophil gelatinase-associated lipocalin, Interleukin-18, Kidney injury molecule-1, and Liver fatty acid-binding protein. In conclusion, we suggest the need for further meta-analyses with the availability of additional studies.

Hypophosphatemia in acute liver failure of a broad range of etiologies is associated with phosphaturia without kidney damage or phosphatonin elevation

Hypophosphatemia is a common and dangerous complication of acute liver failure (ALF) of various etiologies. While various mechanisms for ALF-associated hypophosphatemia have been proposed including high phosphate uptake into regenerating hepatocytes, acetaminophen (APAP)-associated hypophosphatemia was linked to renal phosphate wasting, and APAP-induced renal tubular injury was proposed as underlying mechanism. We studied 30 normophosphatemic and 46 hypophosphatemic (serum phosphate < 2.5 mg/dL) patients from the Acute Liver Failure Study Group registry with APAP- or non-APAP-induced ALF. Since kidney injury affects phosphate excretion, patients with elevated serum creatinine (>1.2 mg/dL) were excluded. Maximal amount of renal tubular phosphate reabsorption per filtered volume (TmP/GFR) was calculated from simultaneous serum and urine phosphate and creatinine levels to assess renal phosphate handling. Instead of enhanced renal phosphate reabsorption as would be expected during hypophosphatemia of non-renal causes, serum phosphate was positively correlated with TmP/GFR in both APAP- and non-APAP-induced ALF patients (R2 = 0.66 and 0.46, respectively; both P < 0.0001), indicating renal phosphate wasting. Surprisingly, there was no evidence of kidney damage based on urinary markers including neutrophil gelatinase-associated lipocalin and cystatin C even in the APAP group. Additionally, there was no evidence that the known serum phosphatonins parathyroid hormone, fibroblast growth factor 23, and α-Klotho contribute to the observed hypophosphatemia. We conclude that the observed hypophosphatemia with renal phosphate wasting in both APAP- and non-APAP-mediated ALF is likely the result of renal tubular phosphate leak from yet-to-be identified factor(s) with no evidence for proximal tubular damage or contribution of known phosphatonins.

Biomarkers in the clinical management of patients with atrial fibrillation and heart failure

Atrial fibrillation (AF) and heart failure (HF) are two cardiovascular diseases with an increasing prevalence worldwide. These conditions share common pathophysiologiesand frequently co-exit. In fact, the occurrence of either condition can 'cause' the development of the other, creating a new patient group that demands different management strategies to that if they occur in isolation. Regardless of the temproral association of the two conditions, their presence is linked with adverse cardiovascular outcomes, increased rate of hospitalizations, and increased economic burden on healthcare systems. The use of low-cost, easily accessible and applicable biomarkers may hasten the correct diagnosis and the effective treatment of AF and HF. Both AF and HF effect multiple physiological pathways and thus a great number of biomarkers can be measured that potentially give the clinician important diagnostic and prognostic information. These will then guide patient centred therapeutic management. The current biomarkers that offer potential for guiding therapy, focus on the physiological pathways of miRNA, myocardial stretch and injury, oxidative stress, inflammation, fibrosis, coagulation and renal impairment. Each of these has different utility in current clinincal practice.

Diagnosis of Cardiac Surgery-Associated Acute Kidney Injury

Acute kidney injury after cardiac surgery is characterized by specific patterns of damage and recovery that are important to consider for management and outcome. The Kidney Disease: Improving Global Outcomes (KDIGO) classification covers only part of the conceptual framework and is thus insufficient for a comprehensive diagnosis. This review highlights the strengths and limitations of the recent criteria and provides an overview of biomarkers of cardiac surgery-associated acute kidney injury (CSA-AKI). The evolving understanding of CSA-AKI as a time-sensitive condition has increased the demand to enhance the diagnostic criteria and translate biomarkers into clinical practice.

Biomarkers in Acute Kidney Injury

Biomarkers have become a pillar of precision medicine in acute kidney injury (AKI). Traditional markers for diagnosis of AKI are insensitive and insufficient to provide comprehensive information for prognostication. Several emerging biomarkers have shown promising results in large-scale clinical studies. These novel markers likely will be beneficial for personalized AKI prevention and treatment.

Intermittent Urine Oxygen Tension Monitoring for Predicting Acute Kidney Injury After Cardiovascular Surgery: A Preliminary Prospective Observational Study

Introduction

Novel biomarkers of acute kidney injury (AKI) are being developed and commercialized. However, none are universally available. The aim of this preliminary prospective observational study was to explore the effectiveness of intermittent urine oxygen tension (PuO₂) monitoring without special equipment (using a blood gas analyzer) for predicting AKI after elective cardiovascular surgery requiring cardiopulmonary bypass (CPB).

Methods

Fifty patients who underwent elective cardiovascular surgery requiring CPB were enrolled in the study with written informed consent. Urine samples were intermittently collected from a urethral catheter at four points: T1, immediately after induction of general anesthesia in the operating room; T2, immediately after intensive care unit (ICU) admission; T3, six hours after ICU admission; and T4, 12 hours after ICU admission. PuO₂ was measured with a blood gas analyzer. The Kidney Disease Improving Global Outcomes classification was used for the diagnosis of AKI, then patients were followed up until postoperative day 7. By generating the receiver operating characteristic curves, the cut-off value of PuO₂ and area under the curve (AUC) for predicting the onset of AKI was calculated. The odds ratio (OR) and 95% confidence interval (CI) of each time point were calculated using logistic regression analysis or exact logistic regression method. P < 0.05 was considered significant.

Results

Twelve patients were diagnosed with AKI (24% morbidity). The cut-off values of PuO₂ for predicting onset of AKI at the four time points were T1, PuO₂ ≥ 132.4 mmHg (OR 3.1, 95% CI 0.78-12.0, p = 0.11, AUC 0.57); T2, PuO₂ ≥ 153.3 mmHg (OR 5.8, 95% CI 1.08-31.4, p = 0.04, AUC 0.51); T3, PuO₂ ≥ 130.1 mmHg (OR 0.19, 95% CI 0.05-0.75, p = 0.018, AUC 0.68); T4, PuO₂ ≥ 88.6 mmHg (OR 0.07, 95% CI 0-0.486, p = 0.011, AUC 0.64).

Conclusion

Intermittent PuO₂ values at six and 12 hours after ICU admission may be predictors of AKI, although the AUCs to predict AKI were low (0.68 and 0.64). AKI prediction by PuO₂ was not possible immediately after induction of general anesthesia (not statistically significant) and immediately after ICU admission (AUC was very low). Further studies are required to confirm the validity of intermittent PuO₂ monitoring.

Plasma Neutrophil Gelatinase-Associated Lipocalin Is Useful for Predicting Mortality in Critically Ill Patients

Elevated neutrophil gelatinase-associated lipocalin (NGAL) occurs in a wide range of systemic diseases. This study examined the clinical utility of plasma NGAL to predict intensive care unit (ICU) and in-hospital mortality in critically ill patients. A total of 62 patients hospitalized in a mixed ICU were included; pNGAL, creatinine, and C-reactive protein (CRP) were assayed on four consecutive days (D1-D4) following ICU admission. APACHE II score (Acute Physiology and Chronic Health Evaluation) was calculated 24 h post-admission. ICU mortality reached 35% and in-hospital mortality was 39%. The median pNGAL at admission was 142.5 (65.6-298.3) ng/mL. pNGAL was significantly higher in non-survivors compared to survivors. The highest accuracy for ICU mortality prediction was achieved at the pNGAL cutoff of 93.91 ng/mL on D4 area under the curve (AUC) = 0.89; 95%CI 0.69-0.98 and for in-hospital mortality prediction was achieved at the pNGAL cutoff of 176.64 ng/mL on D3 (AUC = 0.86; 95%CI 0.69-0.96). The APACHE II score on ICU admission predicted ICU mortality with AUC = 0.89 (95%CI 0.79-0.96) and in-hospital mortality with AUC = 0.86 (95%CI 0.75-0.94). Although pNGAL on D1 poorly correlated with APACHE II (R = 0.3; p = 0.01), the combination of APACHE II and pNGAL on D1 predicted ICU mortality with AUC = 0.90 (95%CI 0.79-0.96) and in-hospital mortality with AUC = 0.95 (95%CI 0.78-0.99). Maximal CRP during study observation failed to predict ICU mortality (AUC = 0.62; 95%CI 0.49-0.74), but helped to predict in-hospital mortality (AUC = 0.67; 95%CI 0.54-0.79). Plasma NGAL with combination with the indices of critical illness is a useful biomarker for predicting mortality in heterogeneous population of ICU patients.

Acute kidney injury after lung transplantation: a narrative review

Acute kidney injury (AKI) is a commonly recognized complication after lung transplantation (LT) and is related to increased mortality and morbidity. With the improvement of survival after LT and the increasing number of lung transplant recipients, the detrimental impact of current management on renal function has become increasingly apparent. Multifarious risk factors in the perioperative setting contribute to the development of AKI, including the preoperative status and complications of the recipient, complex perioperative problems especially hemodynamic fluctuation, and exposure to nephrotoxic agents, mainly calcineurin inhibitors (CNIs) and antimicrobial drugs. Identification and minimization of the effects of these risk factors can relieve AKI severity and incidence in high-risk patients. Close monitoring of urine output and serum creatinine (sCr) levels and of specific biomarkers may promote early recognition of AKI and rapid nephrology intervention to improve outcomes. This review summarizes advances in the epidemiology, diagnostic criteria, biological markers of AKI, and further recommends appropriate treatment strategies for the long-term management of AKI related manifestations in lung transplant recipients. Future work will need to focus on developing more accurate measures of renal function and identifying patients before the occurrence of early renal damage. Combining renal protection strategies with the use of new biomarkers to develop early kidney risk identification and protection protocols is a promising idea that requires further investigation.

Newer Volatile Anesthetic Agents in Cardiac Anesthesia: Review of Literature

Myocardial protection with volatile anesthetic agents have been suggested by multiple studies. These studies, however, are scattered and are often limited to a particular aspect of cardiac anesthesia. Older inhalational agents like halothane is known to cause significant hepatic damage in patients undergoing long duration surgeries while isoflurane is known to have marked vasodilating properties that also affects the coronary arteries leading to coronary “steal” phenomenon. Additionally, newer agents, like sevoflurane and desflurane, have shown more prominent cardioprotective effects than older agents. We searched ScholarOne, Medline, Embase, and the Cochrane Central Register of Controlled Trials (CENTRAL) in the Cochrane Library. The medical subject headings (MeSH) terms “anaesthesia, inhalational,” “anaesthesia, intravenous, or TIVA,” and “Cardiac anaesthesia or Cardiac Surgery” were used. Additional studies were identified by review of the reference sections of all eligible studies. The aim of this review article is to bring together the evidences with newer inhalational agents and provide a holistic view of their benefits and shortcomings in cardiac anesthesia.

Comprehensive Comparisons among Inotropic Agents on Mortality and Risk of Renal Dysfunction in Patients Who Underwent Cardiac Surgery: A Network Meta-Analysis of Randomized Controlled Trials

Several kinds of inotropes have been used in critically ill patients to improve hemodynamics and renal dysfunction after cardiac surgery; however, the treatment strategies for reducing mortality and increasing renal protection in patients who underwent cardiac surgery remain controversial. Therefore, we performed a comprehensive network meta-analysis to overcome the lack of head-to-head comparisons. A systematic database was searched up to 31 December 2020, for randomized controlled trials that compared different inotropes on mortality outcomes and renal protective effects after cardiac surgery. A total of 29 trials were included and a frequentist network meta-analysis was performed. Inconsistency analyses, publication bias, and subgroup analyses were also conducted. Compared with placebo, use of levosimendan significantly decreased the risks of mortality (odds ratio (OR): 0.74; 95% confidence interval (CI): 0.56–0.97) and risk of acute renal injury (OR: 0.61; 95% CI: 0.45–0.82), especially in low systolic function patients. Use of levosimendan also ranked the best treatment based on the P-score (90.1%), followed by placebo (64.5%), milrinone (49.6%), dopamine (49.5%), dobutamine (29.1%), and fenoldopam (17.0%). Taking all the available data into consideration, levosimendan was a safe renal-protective choice for the treatment of patients undergoing cardiac surgery, especially for those with low systolic function.

A Review of Specific Biomarkers of Chronic Renal Injury and Their Potential Application in Nonclinical Safety Assessment Studies

A host of novel renal biomarkers have been developed over the past few decades which have enhanced monitoring of renal disease and drug-induced kidney injury in both preclinical studies and in humans. Since chronic kidney disease (CKD) and acute kidney injury (AKI) share similar underlying mechanisms and the tubulointerstitial compartment has a functional role in the progression of CKD, urinary biomarkers of AKI may provide predictive information in chronic renal disease. Numerous studies have explored whether the recent AKI biomarkers could improve upon the standard clinical biomarkers, estimated glomerular filtration rate (eGFR), and urinary albumin to creatinine ratio, for predicting outcomes in CKD patients. This review is an introduction to alternative assays that can be utilized in chronic (>3 months duration) nonclinical safety studies to provide information on renal dysfunction and to demonstrate specific situations where these assays could be utilized in nonclinical drug development. Novel biomarkers such as symmetrical dimethyl arginine, dickkopf homolog 3, and cystatin C predict chronic renal injury in animals, act as surrogates for GFR, and may predict changes in GFR in patients over time, ultimately providing a bridge from preclinical to clinical renal monitoring.

A long journey for acute kidney injury biomarkers

Acute kidney injury (AKI) is a life-threatening illness that continues to have an in-hospital mortality rate of patients with AKI ranges from 20% to 50% or greater, depending on underlying conditions. However, it has only marginally declined over the past 25 years. Previous authoritative publications have been pointed out that the lack of useful biomarkers for AKI has limited progress in improving the outcomes of this disorder. The purpose of this paper is to review the recent biomarkers involved in the early detection of AKI and main reasons for the failure to identify new AKI biomarkers. So far, several new AKI biomarkers have been discovered and validated to improve early diagnosis, degree of severity, pathophysiology, differential diagnosis, prediction for major kidney adverse events (MAKE, risk groups for progressive renal failure, need for renal replacement therapy [RRT], or death). These biomarkers can be classified into functional, damage and pre-injury phase biomarkers. However, the clinical use of the studied biomarkers in AKI prediction remains unclear because large prospective multicenter trials have failed to demonstrate troponin-like diagnostic performance. Reasons for the failure to identify AKI biomarkers are the heterogeneity of AKI itself, biomarker limitations and long roads to the validation of candidates for new AKI biomarkers. In an effort to overcome these barriers to identifying new AKI biomarkers, kidney biopsy specimens should be obtained and assessed in human AKI populations. Research in this field should be carried out in a pan-social approach rather than conducted by just a few medical institutions.

Neutrophil Gelatinase-associated Lipocalin as a Marker of Postoperative Acute Kidney Injury Following Cardiac Surgery in Patients with Preoperative Kidney Impairment

INTRODUCTION

Acute kidney injury (AKI) is a serious complication of cardiac surgery. The current 'gold standard' for determining AKI is change in serum creatinine and urine output, however, this change occurs relatively late after the actual injury occurs. Identification of new biomarkers that detect early AKI is required. Recently, new biomarkers, such as the NephroCheck® Test and AKIRisk have also been tested and found to be good indicators of AKI. Neutrophil gelatinase-associated lipocalin (NGAL) has shown promise in paediatric patients but has displayed varied results in adult populations, particularly post cardiac surgery. The aim of this study was to assess the value of urinary NGAL as a biomarker of AKI in patients with pre-existing renal impairment (eGFR >15ml/min to eGFR<60ml/min).

METHODS

A post-hoc analysis of urinary NGAL concentrations from 125 patients with pre-existing kidney impairment, who participated in a randomised trial of haemofiltration during cardiac surgery, was undertaken. Urinary NGAL was measured using ELISA at baseline, post-operatively and 24 and 48 hours after surgery, and serum creatinine was measured pre and postoperatively and then at 24, 48, 72 and 96 hours as routine patient care. NGAL concentrations were compared in patients with and without AKI determined by changes in serum creatinine concentrations. A Kaplan-Meier plot compared survival for patients with or without AKI and a Cox proportional hazards analysis was performed to identify factors with the greatest influence on survival.

RESULTS

Following surgery, 43% of patients developed AKI (based on KDIGO definition). Baseline urinary NGAL was not found to be significantly different between patients that did and did not develop AKI. Urinary NGAL concentration was increased in all patients following surgery, regardless of whether they developed AKI and was also significant between groups at 24 (p=0.003) and 48 hours (p<0.0001). Urinary NGAL concentrations at 48 hours correlated with serum creatinine concentrations at 48 hours (r=0.477, p<0.0001), 72 hours (r=0.488, p<0.0001) and 96 hours (r=0.463, p<0.0001). Urinary NGAL at 48 hours after surgery strongly predicted AKI (AUC=0.76; P=0.0001). A Kaplan- Meier plot showed that patients with postoperative AKI had a significantly lower 7-year survival compared with those without AKI. Postoperative urinary NGAL at 48 hours >156ng/mL also strongly predicted 7-year survival. However, additive EuroSCORE, age, current smoking and post-operative antibiotics usage were distinctly significantly more predictive of 7-year survival as compared with postoperative urinary NGAL at 48 hours >156ng/mL.

CONCLUSIONS

Our study demonstrated that postoperative urinary NGAL levels at 48 hours postsurgery strongly predicts the onset or severity of postoperative AKI based on KDIGO classification in patients with preoperative kidney impairment and were also strongly related to 7-year survival.

Will urinary biomarkers provide a breakthrough in diagnosing cardiac surgery-associated AKI? - A systematic review

Introduction: Acute kidney injury following cardiac surgery is a dreaded complication contributing to early mortality. Diagnosing AKI using serum creatinine usually results in a delay. To combat this, certain kidney damage specific biomarkers were investigated to identify if they can serve as early predictors of cardiac surgery-associated AKI (CSA-AKI). This study systematically reviews three such biomarkers; NGAL, tissue inhibitor of matrix metalloproteinase-2 (TIMP-2) and insulin-like growth factor binding protein-7 (IGFBP7) to identify if they can serve as early predictors of CSA-AKI.Methods: Systematic search was carried out on literature reporting the diagnostic ability of the three biomarkers from databases in accordance with PRISMA guidelines.Results: We found 43 articles reporting urinary-NGAL levels (n = 34 in adults, n = 9 in children) and 10 studies reporting TIMP-2 and IGFBP7 levels among adults. Interestingly, NGAL showed high diagnostic value in predicting AKI in children (seven among nine studies with AUROC > 0.8). The cell cycle arrest biomarkers, namely TIMP-2 and IGFBP7, showed high diagnostic value in predicting AKI in adults (five among ten studies with AUROC > 0.8).Conclusion: In predicting CSA-AKI; the diagnostic value of NGAL is high in the paediatric population while the diagnostic value of TIMP-2 and IGFBP7 is high in adults.

Diagnostic and Therapeutic Potential of microRNAs in Acute Kidney Injury

During hospital stay, about 20% of adult patients experience an episode of acute kidney injury (AKI), which is characterized by a rapid decrease in kidney function. Diagnostic tools regarding early diagnosis of kidney dysfunction prior to AKI and markers of renal recovery are not available. Additionally, there is no therapeutic option for the treatment of AKI. Thus, better and more specific diagnostic and therapeutic options are urgently needed in daily clinical practice. NoncodingRNAs (ncRNAs) have come into focus of research in the context of AKI in the last decade. The best characterized group of ncRNAs are microRNAs (miRNAs). An increasing body of literature has shown that miRNAs are involved in the pathogenesis of AKI and that they are promising future tools in the diagnosis and therapy of AKI. However, there are obstacles to be overcome before miRNAs can be transferred to patient care. This review will give an overview of our current knowledge of miRNA involvement in the context of AKI while critically evaluating their diagnostic and therapeutic potential.

Biomarkers of Acute and Chronic Kidney Disease

The current unidimensional paradigm of kidney disease detection is incompatible with the complexity and heterogeneity of renal pathology. The diagnosis of kidney disease has largely focused on glomerular filtration, while assessment of kidney tubular health has notably been absent. Following insult, the kidney tubular cells undergo a cascade of cellular responses that result in the production and accumulation of low-molecular-weight proteins in the urine and systemic circulation. Modern advancements in molecular analysis and proteomics have allowed the identification and quantification of these proteins as biomarkers for assessing and characterizing kidney diseases. In this review, we highlight promising biomarkers of kidney tubular health that have strong underpinnings in the pathophysiology of kidney disease. These biomarkers have been applied to various specific clinical settings from the spectrum of acute to chronic kidney diseases, demonstrating the potential to improve patient care.

Biomarker-guided implementation of the KDIGO guidelines to reduce the occurrence of acute kidney injury in patients after cardiac surgery (PrevAKI-multicentre): protocol for a multicentre, observational study followed by randomised controlled feasibility trial

INTRODUCTION

Acute kidney injury (AKI) is a frequent complication after cardiac surgery with adverse short-term and long-term outcomes. Although prevention of AKI (PrevAKI) is strongly recommended, the optimal strategy is uncertain. The Kidney Disease: Improving Global Outcomes (KDIGO) guideline recommended a bundle of supportive measures in high-risk patients. In a single-centre trial, we recently demonstrated that the strict implementation of the KDIGO bundle significantly reduced the occurrence of AKI after cardiac surgery. In this feasibility study, we aim to evaluate whether the study protocol can be implemented in a multicentre setting in preparation for a large multicentre trial.

METHODS AND ANALYSIS

We plan to conduct a prospective, observational survey followed by a randomised controlled, multicentre, multinational clinical trial including 280 patients undergoing cardiac surgery with cardiopulmonary bypass. The purpose of the observational survey is to explore the adherence to the KDIGO recommendations in routine clinical practice. The second phase is a randomised controlled trial. The objective is to investigate whether the trial protocol is implementable in a large multicentre, multinational setting. The primary endpoint of the interventional part is the compliance rate with the protocol. Secondary endpoints include the occurrence of any AKI and moderate/severe AKI as defined by the KDIGO criteria within 72 hours after surgery, renal recovery at day 90, use of renal replacement therapy (RRT) and mortality at days 30, 60 and 90, the combined endpoint major adverse kidney events consisting of persistent renal dysfunction, RRT and mortality at day 90 and safety outcomes.

ETHICS AND DISSEMINATION

The PrevAKI multicentre study has been approved by the leading Research Ethics Committee of the University of Münster and the respective Research Ethics Committee at each participating site. The results will be used to design a large, definitive trial.

TRIAL REGISTRATION NUMBER

NCT03244514.

Proteinuria-take a closer look!

Proteinuria is a hallmark of kidney disease. Therefore, measurement of urine protein content plays a central role in any diagnostic work-up for kidney disease. In many cases, proteinuria analysis is restricted to the measurement of total protein content knowing that very high levels of proteinuria (nephrotic proteinuria) are characteristic of glomerular disease. Still, proteinuria can also be a manifestation of impaired tubular protein reabsorption or even be physiological. This review will discuss the physiology of renal protein handling and give guidance on a more sophisticated analysis of proteinuria differentiating albumin, low-molecular weight proteins and immunoglobulins. These non-invasive tests are available in most routine clinical laboratories and may guide the clinician in the diagnostic process before ordering far more expensive (molecular genetic testing) and/or invasive (kidney biopsy) diagnostics.

Perioperative Acute Kidney Injury

Perioperative organ injury is among the leading causes of morbidity and mortality of surgical patients. Among different types of perioperative organ injury, acute kidney injury occurs particularly frequently and has an exceptionally detrimental effect on surgical outcomes. Currently, acute kidney injury is most commonly diagnosed by assessing increases in serum creatinine concentration or decreased urine output. Recently, novel biomarkers have become a focus of translational research for improving timely detection and prognosis for acute kidney injury. However, specificity and timing of biomarker release continue to present challenges to their integration into existing diagnostic regimens. Despite many clinical trials using various pharmacologic or nonpharmacologic interventions, reliable means to prevent or reverse acute kidney injury are still lacking. Nevertheless, several recent randomized multicenter trials provide new insights into renal replacement strategies, composition of intravenous fluid replacement, goal-directed fluid therapy, or remote ischemic preconditioning in their impact on perioperative acute kidney injury. This review provides an update on the latest progress toward the understanding of disease mechanism, diagnosis, and managing perioperative acute kidney injury, as well as highlights areas of ongoing research efforts for preventing and treating acute kidney injury in surgical patients.

Biomarkers in Acute Kidney Injury

How to cite this article: Bhosale SJ, Kulkarni AP. Biomarkers in Acute Kidney Injury. Indian J Crit Care Med 2020;24(Suppl 3):S90-S93.

Prediction Efficiency of Postoperative Acute Kidney Injury in Acute Stanford Type A Aortic Dissection Patients with Renal Resistive Index and Semiquantitative Color Doppler

Objectives

This study is aimed to evaluate the efficiency in early prediction of postoperative persistent acute kidney injury (PAKI) after surgery in acute Stanford type A aortic dissection (AAAD) patients by using Doppler renal resistive index (RRI) and semiquantitative color (SQC) Doppler grade, respectively.

Methods

84 AAAD patients received Sun's surgical management, and 67 patients were enrolled. RRI and SQC Doppler grade were evaluated by ultrasonography, respectively, at 6 hours after surgery. Serum creatinine (sCr) was recorded before operation and at 24 hours, 48 hours, and 72 hours after operation. AKI grade was evaluated according to the classifications of the Acute Kidney Injury Network (AKIN). PAKI is defined as persistent oliguria and/or sCr elevation after 3 days. RRI and SQC Doppler grade were compared, respectively, between the PAKI and non-PAKI groups. Potential predictors were first tested by univariate logistic regression analysis, and a multivariate model was identified to determine the independent predictive ability of RRI and SQC Doppler grade for the PAKI. Receiver operating characteristic (ROC) analysis was performed to compare the diagnostic accuracy between RRI and SQC Doppler grade in early prediction of PAKI by using AKIN classifications as the reference standard.

Results

Of a total of 67 patients enrolled during the study period, 21 (31.3%) patients suffered from PAKI and 8 (11.9%) patients required dialysis. There are significant differences in RRI (0.80 ± 0.09 vs. 0.70 ± 0.05, P=0.002) and SQC Doppler grade (x²=12.193, P=0.007) between the 2 groups with and without PAKI. Univariate analysis showed that RRI, SQC Doppler grade, length of stay in ICU, time of CPB, and length of stay in hospital were significant predictors of PAKI. RRI and the SQC Doppler grade remained independent predictors of PAKI. Area under the curve (AUC) of RRI was 0.855 (95% CI, 0.74–0.96) with cutoff value 0.725 (sensitivity 90.9% and specificity 71.1%), AUC of SQC Doppler grade was 0.642 (95% CI, 0.49–0.79) with cutoff value grade 2 (sensitivity 50% and specificity 73.3%).

Conclusion

Both postoperative RRI and SQC Doppler grade are independent predictors for PAKI after surgery in AAAD patients. Both postoperative RRI and SQC Doppler grade can be obtained rapidly by bedside ultrasound, which is a good tool for early prediction for postoperative PAKI.

Impact of Custodiol-N cardioplegia on acute kidney injury after cardiopulmonary bypass

Myocardial protection during cardiopulmonary bypass (CPB) can be achieved using cardioplegic solutions. Although, acute kidney injury (AKI) is a common complication following CPB, the effects of cardioplegic solutions on AKI have rarely been investigated. Within this study, the effects of the cardioplegic solutions histidine-tryptophan-ketoglutarate (HTK; Custodiol) and HTK-N (Custodiol-N) on AKI in a large animal model were compared. Therefore, Landrace pigs underwent median sternotomy, CPB at 34°C, 90 minutes of cardiac arrest and 120 minutes of reperfusion. Animals were randomized for single-shot cardioplegia with either HTK (n = 10) or HTK-N (n = 10). Renal biopsies and sera were analyzed to determine AKI biomarkers and apoptosis. Compared to HTK, HTK-N induced a decreased extent of proximal tubule swelling (48.3 ± 1.6 µm vs 52.3 ± 1.1 µm, P = .05) and decreased cytochrome c release (0.26 ± 0.04 vs 0.46 ± 0.08, P = .04) without reaching statistical significance due to Bonferroni correction. Comparing baseline and postreperfusion levels, the hemoglobin (Hb) and blood calcium levels were lower in HTK-N (Hb_baseline : 6.0 ± 0.6 mmol/L, Hb_reperfusion : 6.2 ± 0.7 mmol/L, P = .12; Ca²⁺ _baseline : 1.36 ± 0.05 mmol/L, Ca²⁺ _reperfusion : 1.28 ± 0.05 mmol/L, P = .16) compared to the HTK group (Hb_baseline : 5.9 ± 0.4 mmol/L, Hb_reperfusion : 4.7 ± 0.8 mmol/L, P < .01; Ca²⁺ _baseline : 1.34 ± 0.07 mmol/L, Ca²⁺ _reperfusion : 1.24 ± 0.06 mmol/L, P < .01). The present study showed that HTK-N could positively affect the kidney during CPB. Hb and calcium levels were stabilized. A statistical trend was found showing that AKI-related proximal tubule swelling and cytochrome c release were diminished.

Noncoding RNAs in acute kidney injury

Acute kidney injury (AKI) is an important health issue concerning ∼50% of patients treated in intensive care units. AKI mainly occurs after sepsis, acute ischemia, nephrotoxicity, or hypoxia and leads to severe damage of the kidney and to an increased risk of mortality. The diagnosis of AKI is currently based on creatinine urea levels and diuresis. Yet, novel markers may improve the accuracy of this diagnosis at an early stage of the disease, thereby allowing early prevention and therapy, ultimately leading to a reduction in the need for renal replacement therapy and decreased mortality. Non-protein-coding RNAs or noncoding RNAs are central players in development and disease. They are important regulatory molecules that allow a fine-tuning of gene expression and protein synthesis. This regulation is necessary to maintain homeostasis, and its dysregulation is often associated with disease development. Noncoding RNAs are present in the kidney and in body fluids and their expression is modulated during AKI. This review article assembles the current knowledge of the role of noncoding RNAs, including microRNAs, long noncoding RNAs and circular RNAs, in the pathogenesis of AKI. Their potential as biomarkers and therapeutic targets as well as the challenges to translate research findings to clinical application are discussed. Although microRNAs have entered clinical testing, preclinical and clinical trials are needed before long noncoding RNAs and circular RNAs may be considered as useful biomarkers or therapeutic targets of AKI.

Acute kidney injury after cardiac surgery: prevalence, impact and management challenges

Acute kidney injury (AKI) is a major medical problem that is of particular concern after cardiac surgery. Perioperative AKI is independently associated with an increase in short-term morbidity, costs of treatment, and long-term mortality. In this review, we explore the definition of cardiac surgery-associated acute kidney injury (CSA-AKI) and identify diverse mechanisms and risk factors contributing to the renal insult. Current theories of the pathophysiology of CSA-AKI and description of its clinical course will be addressed in this review. Data on the most promising renal protective strategies in cardiac surgery, from well-designed studies, will be scrutinized. Furthermore, diagnostic tools such as novel biomarkers of AKI and their potential utility will be discussed.

Higher arterial pressure during cardiopulmonary bypass may not reduce the risk of acute kidney injury

Background

Acute kidney injury after cardiac surgery is common and associated with increased mortality. It is unknown whether an intended higher arterial pressure during cardiopulmonary bypass reduces the incidence of acute and chronic kidney injury.

Methods

Patients were randomised either to a control group or a high pressure group (arterial pressure > 60 mmHg). The inclusion criteria were age > 70 years, combined cardiac surgery and serum creatinine < 200 μmol/L. Glomerular filtration rate using the Cr-EDTA clearance method was measured the day before surgery and 4 months postoperatively. The RIFLE criteria were used to define the presence of acute kidney injury. In addition, the ratio between urinary Neutrophil Gelatinase-Associated Lipocalin (NGAL) and creatinine was measured.

Results

Ninety patients were included. Mean age was 76 ± 4 years and 76% were male. Mean arterial pressure was 47 ± 5 mmHg in the control group and 61 ± 4 mmHg in the high pressure group (p < 0.0001). The change in glomerular filtration rate at follow-up was − 9 ± 12 ml/min in the control group and − 5 ± 16 ml/min in the high pressure group (p = 0.288, 95% CI − 13 to 4). According to the RIFLE criteria 38% in the control group and 46% in the high pressure group developed acute kidney injury (p = 0.447). The postoperative urinary NGAL/creatinine ratio was comparable between the groups.

Conclusions

An intended increase in arterial pressure during cardiopulmonary bypass to > 60 mmHg did not decrease the incidence of acute or chronic kidney injury after cardiac surgery.

Trial registration

Clinicaltrials.gov, identifier: NCT01408420. Registered 3rd of August 2011.

Urinary and Serum Biomarkers for Prediction of Acute Kidney Injury in Patients Undergoing Liver Transplantation

Acute kidney injury (AKI) is a frequent and serious complication of orthotopic liver transplantation (OLT), with a significant impact on mortality, graft survival, and chronic kidney disease. Currently, the diagnosis of AKI is based on changes in serum creatinine, which is a late marker, usually rising when there is already significant damage to the renal parenchyma. During the last 2 decades, various biomarkers have been studied in many clinical situations, mostly after cardiac surgery, in drug-induced AKI, or in sepsis. The present article summarizes the data on those biomarkers that have been evaluated for the prediction of AKI in patients undergoing OLT.

Urinary Nephrin as a Biomarker of Glomerular Maturation and Injury Is Associated with Acute Kidney Injury and Mortality in Critically Ill Neonates

BACKGROUND

Nephrin is a key component of the slit diaphragm of the glomerular podocyte, and increased urinary nephrin level may reflect glomerular injury.

OBJECTIVES

To determine whether urinary nephrin is a useful biomarker of glomerular maturation and injury and whether it is associated with acute kidney injury (AKI) and neonatal intensive care unit (NICU) mortality in critically ill neonates.

METHODS

Urinary samples were serially collected in 234 neonates during NICU stay for measurements of nephrin, cystatin C (CysC), and albumin. AKI diagnosis was based on neonatal Kidney Disease: Improving Global Outcome (KDIGO) criteria.

RESULTS

Of the neonates, 26 developed AKI and 24 died during NICU stay. The independent contributors to the initial urinary nephrin level obtained on the first 24 h admitted to NICU were gestational age (p = 0.004) and initial urinary CysC level (p < 0.001). Both initial (p = 0.037) and peak (p = 0.039) urinary nephrin were significantly associated with AKI, even after controlling for significant covariates, and had an area under the receiver-operating characteristic curve (AUC) of 0.71 and 0.70, respectively, for predicting AKI. At the optimal cutoff value of 0.375 μg/mg urinary creatinine, the initial urinary nephrin displayed sensitivity of 61.5% and specificity of 76.9% for predicting AKI. The AUCs for initial and peak urinary nephrin to predict NICU mortality were 0.81 and 0.83, respectively.

CONCLUSIONS

Urinary nephrin, which may decrease with increasing glomerular maturity, is significantly associated with increased risk for AKI and NICU mortality even after adjustment for potential confounders. A higher level of urinary nephrin may be independently predictive of AKI and NICU mortality in critically ill neonates.

The future for diagnostic tests of acute kidney injury in critical care: evidence synthesis, care pathway analysis and research prioritisation

BACKGROUND

Acute kidney injury (AKI) is highly prevalent in hospital inpatient populations, leading to significant mortality and morbidity, reduced quality of life and high short- and long-term health-care costs for the NHS. New diagnostic tests may offer an earlier diagnosis or improved care, but evidence of benefit to patients and of value to the NHS is required before national adoption.

OBJECTIVES

To evaluate the potential for AKI in vitro diagnostic tests to enhance the NHS care of patients admitted to the intensive care unit (ICU) and identify an efficient supporting research strategy.

DATA SOURCES

We searched ClinicalTrials.gov, The Cochrane Library databases, Embase, Health Management Information Consortium, International Clinical Trials Registry Platform, MEDLINE, metaRegister of Current Controlled Trials, PubMed and Web of Science databases from their inception dates until September 2014 (review 1), November 2015 (review 2) and July 2015 (economic model). Details of databases used for each review and coverage dates are listed in the main report.

REVIEW METHODS

The AKI-Diagnostics project included horizon scanning, systematic reviewing, meta-analysis of sensitivity and specificity, appraisal of analytical validity, care pathway analysis, model-based lifetime economic evaluation from a UK NHS perspective and value of information (VOI) analysis.

RESULTS

The horizon-scanning search identified 152 potential tests and biomarkers. Three tests, Nephrocheck^® (Astute Medical, Inc., San Diego, CA, USA), NGAL and cystatin C, were subjected to detailed review. The meta-analysis was limited by variable reporting standards, study quality and heterogeneity, but sensitivity was between 0.54 and 0.92 and specificity was between 0.49 and 0.95 depending on the test. A bespoke critical appraisal framework demonstrated that analytical validity was also poorly reported in many instances. In the economic model the incremental cost-effectiveness ratios ranged from £11,476 to £19,324 per quality-adjusted life-year (QALY), with a probability of cost-effectiveness between 48% and 54% when tests were compared with current standard care.

LIMITATIONS

The major limitation in the evidence on tests was the heterogeneity between studies in the definitions of AKI and the timing of testing.

CONCLUSIONS

Diagnostic tests for AKI in the ICU offer the potential to improve patient care and add value to the NHS, but cost-effectiveness remains highly uncertain. Further research should focus on the mechanisms by which a new test might change current care processes in the ICU and the subsequent cost and QALY implications. The VOI analysis suggested that further observational research to better define the prevalence of AKI developing in the ICU would be worthwhile. A formal randomised controlled trial of biomarker use linked to a standardised AKI care pathway is necessary to provide definitive evidence on whether or not adoption of tests by the NHS would be of value.

STUDY REGISTRATION

The systematic review within this study is registered as PROSPERO CRD42014013919.

FUNDING

The National Institute for Health Research Health Technology Assessment programme.

Kidney Injury Biomarkers in an Academic Hospital Setting: Where Are We Now?

Acute kidney injury (AKI) is a frequent complication in hospitalised patients and is diagnosed by urinary output and serum creatinine. Serum creatinine is an indirect marker for renal glomerular filtration, but lacks specificity for damage to kidney tissue and the relatively late response to injury precludes early recognition of AKI. Timely diagnosis of kidney injury using biomarkers that provide information about the aetiology of kidney injury is an unmet clinical need. To overcome the suboptimal performance of serum creatinine, injury biomarkers have been proposed that predict AKI in diverse clinical settings. The clinical performance of these markers is considered moderate due to the lack of specificity for kidney tissue or the underlying injury mechanisms, poor test specificity and confounding by interventions or comorbidities. Hence, it is not unequivocally beneficial to implement current kidney injury biomarkers in the clinical laboratory for diagnostic purposes. In this article we review biomarkers that might fulfil AKI-related unmet clinical needs in the academic hospital setting.