Recalibration of cystatin C using standardized material in Siemens nephelometers

Long-term kidney outcomes in survivors of Wilms tumor: a single-center retrospective cohort study

BACKGROUND

Several studies have investigated long-term kidney outcomes in survivors of Wilms tumor (WT). However, many have small sample sizes, and there is a wide variation in reported outcomes. The aim of this study is to investigate the long-term kidney outcomes in survivors of WT (S-WT), including those patients considered to be at high risk for poor kidney outcomes, and using updated estimated glomerular filtration rate (eGFR) equations.

METHODS

This was a retrospective chart review of 64 patients treated for WT at a single pediatric center. Patients were off treatment for 5 years or more at the time of analysis and were evaluated for decreased kidney function, hypertension, proteinuria, and compensatory hypertrophy of the contralateral kidney.

RESULTS

At a median follow-up time of 11.3 years off treatment (range 5-22.6) and average age of 16.7 years (range 6.5-30), 35 patients had a decreased eGFR (< 90 mL/min/1.73 m2), and 2 patients had progressed to chronic kidney disease stage 5. Compensatory hypertrophy was observed in 67% of cases. 41% of patients had elevated clinic blood pressures, with 2 patients on an anti-hypertensive medication. Three of 9 patients had evidence of hypertension on ambulatory blood pressure monitoring. Eight of 37 patients (22%) had proteinuria.

CONCLUSIONS

Kidney dysfunction is common in S-WT at a young age. This population should be carefully monitored for the development of decreased eGFR, hypertension, and proteinuria as part of their routine survivorship care. This is particularly true for modifiable risk factors of chronic kidney disease progression, such as hypertension and proteinuria.

Is body composition important in the context of renal function in pediatric neurogenic bladder?

BACKGROUND

Neurogenic bladder due to myelomeningocele (MMC) is a significant risk factor for chronic kidney disease in children. Cystatin C (CysC) is a more accurate GFR marker than creatinine as it is unaffected by muscle mass but may be influenced by fat mass and BMI. This study evaluates: (1) GFR measurement accuracy using CysC and creatinine in MMC-related neurogenic bladder, (2) the relationship between body composition via bioelectrical impedance analysis (BIA) and renal parameters, and (3) the use of BIA for non-invasive GFR and body composition assessment.

METHODS

Forty children (median age 9.96 years) underwent serum creatinine, CysC testing, and BIA measurements. We assessed age, sex, spinal lesion level, anthropometric measurements, BMI, and activity using Hoffer's scale. GFR was calculated using five creatinine-based formulas, three CysC-based, and three combining CysC and creatinine, including BIA GFR as an alternative approach.

RESULTS

Creatinine-based GFR estimates were significantly higher than CysC-based GFR. Although only 30% of MMC patients met the traditional BMI criteria for overweight/obesity, 62.5% were obese based on BIA-measured body fat percentage. Significant differences were found in CysC and CysC-based GFR equations within BMI and fat mass groups. Positive correlations were observed between CysC and body weight, BMI percentiles, body fat mass and fat-to-muscle ratio. Muscle mass positively correlated with creatinine.

CONCLUSIONS

BIA-determined fat mass percentage is a more sensitive obesity indicator than BMI in MMC patients. CysC levels and CysC-based GFR equations are influenced by body fat mass, requiring consideration of adiposity to avoid misestimating renal impairment.

Comparison of three different cystatin C measurement procedures in a pediatric chronic kidney disease cohort: Calibration for longitudinal measurements and implications for clinical estimation of GFR

INTRODUCTION

Serum cystatin C (CysC) is used to estimate glomerular filtration rate (eGFR), including in the Chronic Kidney Disease in Children (CKiD) Under 25 years (U25eGFR) equations. Several CysC measurement procedures available from diagnostic vendors include reference material for calibration, but the extent of heterogeneity across manufacturers is unclear. Since heterogeneity may have clinical and research implications for eGFR, we evaluated three CysC procedures in samples from the CKiD study representing a wide spectrum of kidney function.

MATERIALS AND METHODS

The three CysC measurement procedures evaluated were: Siemens BN II N Latex CystatinC Assay; Gentian CystatinC Immunoassay; and Roche Tina-quant CystatinC Gen.2. Bland-Altman quantified agreement with Siemens as reference because that method was used for longitudinal CKiD samples from 2003 to 2023. We present derivation of the interquartile range (IQR) of U25eGFR as a measure of precision and describe differences outside this range.

RESULTS

From 53 samples from 44 participants, Gentian measurements were 7 % higher than Siemens (95 %CI: +5.6 %,+8.5 %), while Roche measurements were 4.8 % lower on average (95 %CI: -6.2 %,-3.3 %). Both had very high correlation: 0.9926 and 0.9906, respectively. There was strong agreement across procedures, but a simple correction factor of 7 % reduction applied to Gentian yielded unbiased estimates (+0.03 %, 95 %CI: -1.3 %,+1.4 %) and strong performance in Deming regression. For precision, 98 % of U25eGFR values based on Gentian and Roche CysC were each within the IQR of the Siemens-based estimates.

CONCLUSIONS

Despite reference material calibration, heterogeneity across CysC measurement procedures was observed. Procedure variability was within the limits of U25eGFR estimates indicating that practically, all procedures are appropriate for clinical use. Clinicians may consider calculating IQR of U25eGFR estimates for pediatric chronic kidney disease management.

Challenges and Perspectives on the Adoption of Cystatin C testing in China: A laboratory technician's perspective

Cystatin C (CysC) belongs to the cysteine protease inhibitor superfamily and is produced by all nucleated cells in the body in very stable amounts independent of age, sex, diet, and muscle mass. CysC is considered an ideal biomarker for assessing glomerular filtration rate (GFR) compared to traditional biomarkers for assessing GFR, such as creatinine. However, CysC is not sufficiently utilized for GFR assessment by clinicians, probably for various reasons such as insufficient understanding among clinicians or a lack of standardized quantitative methods. This review discusses and analyzes the aforementioned issues from the perspective of laboratory technicians.

Comparison of estimated GFR using cystatin C versus creatinine in pediatric kidney transplant recipients

BACKGROUND

An accurate, rapid estimate of glomerular filtration rate (GFR) in kidney transplant patients affords early detection of transplant deterioration and timely intervention. This study compared the performance of serum creatinine (Cr) and cystatin C (CysC)-based GFR equations to measured GFR (mGFR) using iohexol among pediatric kidney transplant recipients.

METHODS

CysC, Cr, and mGFR were obtained from 45 kidney transplant patients, 1-18 years old. Cr- and CysC-estimated GFR (eGFR) was compared against mGFR using the Cr-based (Bedside Schwartz, U25-Cr), CysC-based (Gentian CysC, CAPA, U25-CysC), and Cr-CysC combination (CKiD Cr-CysC, U25 Cr-CysC) equations in terms of bias, precision, and accuracy. Bland-Altman plots assessed the agreement between eGFR and mGFR. Secondary analyses evaluated the formulas in patients with biopsy-proven histological changes, and K/DOQI CKD staging.

RESULTS

Bias was small with Gentian CysC (0.1 ml/min/1.73 m2); 88.9% and 37.8% of U25-CysC estimations were within 30% and 10% of mGFR, respectively. In subjects with histological changes on biopsy, Gentian CysC had a small bias and U25-CysC were more accurate-both with 83.3% of and 41.7% of estimates within 30% and 10% mGFR, respectively. Precision was better with U25-CysC, CKiD Cr-CysC, and U25 Cr-CysC. Bland-Altman plots showed the Bedside Schwartz, Gentian CysC, CAPA, and U25-CysC tend to overestimate GFR when > 100 ml/min/1.72 m2. CAPA misclassified CKD stage the least (whole cohort 24.4%, histological changes on biopsy 33.3%).

CONCLUSIONS

In this small cohort, CysC-based equations with or without Cr may have better bias, precision, and accuracy in predicting GFR.

Trajectories of eGFR after kidney transplantation according to trajectories of eGFR prior to kidney replacement therapies in children with chronic kidney disease

BACKGROUND

In children with chronic kidney disease (CKD), certain risk factors are associated with faster eGFR decline and earlier kidney failure. Whether these factors have lingering effects on post-transplant eGFR trajectory remains unclear. We characterized pre- and post-transplant eGFR trajectories in pediatric kidney transplant recipients by their pre-kidney replacement therapy (KRT) risk factors.

METHODS

We studied eGFR trajectories before KRT initiation and after transplantation among Chronic Kidney Disease in Children (CKiD) Study participants. We used mixed-effects models to compare pre-KRT versus post-transplant eGFR trajectories within individual participants by 7 pre-KRT risk factors: glomerular/non-glomerular etiology, race, preemptive transplant, proteinuria, albuminuria, and systolic/diastolic blood pressure (SBP/DBP).

RESULTS

We analyzed 1602 pre-KRT and 592 post-transplant eGFR measurements from 246 transplant recipients. Mean annual eGFR decline was decreased from 18.0% pre-KRT (95%CI, 16.1-19.8) to 5.0% post-transplant (95%CI, 3.3-6.7). All 7 pre-KRT risk factors showed strong associations with faster pre-KRT eGFR decline, but not with post-transplant eGFR decline; only albuminuria, high SBP, and high DBP reached statistical significance with notably attenuated associations. In our multivariable model of the pre-KRT risk factors, post-transplant eGFR decline was more rapid only when albuminuria and high SBP were both present.

CONCLUSIONS

eGFR decline substantially slows down after transplant even among children with rapidly progressing forms of CKD. Nonetheless, those who had albuminuria and high SBP before KRT might continue to show faster eGFR decline after transplant, specifically when both risk factors were present. This subgroup might benefit from intensive pre-transplant management for at least one of the two risk factors. A higher resolution version of the Graphical abstract is available as Supplementary information.

Application of GFR estimating equations to children with normal, near-normal, or discordant GFR

BACKGROUND

The objective was to determine the extent that eGFR formulas correspond to measured plasma iohexol clearance (iGFR) in children with normal or near normal kidney function, particularly how different eGFR formulas yield discordant results.

METHODS

iGFR from 2 (iGFR-2pt) and 4 (iGFR-4pt) time points along with creatinine and/or cystatin C-based eGFR were measured in children with mild CKD, stages 1-2. eGFR was calculated using 6 equations: 3 under 25 (U25) formulas from the Chronic Kidney Disease in Children (CKiD) study, the full age-combined cystatin C (cysC) and creatinine spectrum (FAS-combined), the European Kidney Function Consortium (EKFC-creatinine) equation, and the Chronic Kidney Disease Epidemiology Collaboration (CKD-epi) cysC-based equation.

RESULTS

Twenty-nine children were included, of which 22 had discordant creatinine vs. cystatin C-based eGFR by ≥ 15mL/min/1.73 m2. Overall, the FAS-combined had the least bias, while the U25 most accurately identified children with an eGFR < 90 mL/min/1.73 m2. When Cr-eGFR was ≥ 15 mL/min higher than CysC-eGFR, the U25 creatinine eGFR was closest to iGFR-4pt. When CysC eGFR was higher, the U25-combined was closest to iGFR-4pt.

CONCLUSION

The formulas that most closely approximated the measured GFR varied depending on the pattern of discordant eGFR results. Based on the results, we recommend using the CKiD U25-combined formula to screen for children with a low GFR. Either the CKiD U25-combined or FAS-combined would be recommended for changes in eGFR longitudinally. However, because all formulas were discordant from the iGFR-4pt in over a third of participants, further refinement of pediatric eGFR formulas is needed at the normal/near-normal range. A higher resolution version of the Graphical abstract is available as Supplementary information.

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.

Baseline characteristics of participants enrolled in the KoreaN cohort study for Outcomes in patients With Pediatric Chronic Kidney Disease (KNOW-Ped CKD)

BACKGROUND

We developed the KoreaN cohort study for Outcomes in patients With Pediatric Chronic Kidney Disease (KNOW-Ped CKD) as a subcohort of KNOW-CKD to investigate the different characteristics of pediatric CKD between countries and races.

METHODS

Children aged younger than 18 years with stage 1 ~ 5 CKD were recruited at seven major pediatric nephrology centers in Korea. Blood and urine samples, as well as demographic and clinical data, were collected. From 2011 to 2016, 458 children were enrolled, and the baseline profiles of 437 children were analyzed.

RESULTS

The median age of the cohort was 10.9 years old, and 68.0% were males. The median estimated glomerular filtration rate was 53.1 mL/min/1.73 m². The most common etiology of CKD was congenital anomalies of the kidney and urinary tract (42.6%), followed by glomerulopathies (25.6%).

CONCLUSION

We report a cross-sectional analysis of the overall baseline characteristics such as age, CKD stage, and underlying kidney disease of the KNOW-Ped CKD. The cohort will be longitudinally followed for ten years. "A higher resolution version of the Graphical abstract is available as Supplementary information."

Assessment of Kidney Function in Children

A good understanding of kidney function tests is essential for patient care. Urinalysis is the commonest used test for screening purposes in ambulatory settings. Glomerular function is assessed further by urine protein excretion and estimated glomerular filtration rate and tubular function by various tests such as urine anion gap and excretion of sodium, calcium, and phosphate. In addition, kidney biopsy and/or genetic analyses may be required to further characterize the underlying kidney disease. In this article, we discuss maturation and the assessment of kidney function in children.

Time to Rethink the Current Paradigm for Assessing Kidney Function in Drug Development and Beyond

Chronic kidney disease (CKD) is an important health issue that affects ~ 9.1% of the world adult population. Serum creatinine is the most commonly used biomarker for assessing kidney function and is utilized in different equations for estimating creatinine clearance or glomerular filtration rate (GFR). The Cockcroft-Gault formula for adults and "original" Schwartz formula for children have been the most commonly used equations for estimating kidney function during the last 3-4 decades. Introduction of standardized serum creatinine bioanalytical methodology has reduced interlaboratory variability but is not intended to be used with Cockcroft-Gault or original Schwartz equations. More accurate equations (for instance, Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) for adults and bedside Schwartz or Chronic Kidney Disease in Children Schwartz equation for children) based on standardized serum creatinine values (and another biomarker-cystatin C) have been introduced and validated in recent years. Recently, the CKD-EPI equation refitted without a race variable was introduced. Clinical practice guidance in nephrology advocates a shift to these equations for managing health care of patients with CKD. The guidance also recommends use of albuminuria in addition to GFR for CKD diagnosis and management. Significant research with large data sets would be necessary to evaluate whether this paradigm would also be valuable in drug dose adjustments. This article attempts to highlight some important advancements in the field from a clinical pharmacology perspective and is a call to action to industry, regulators, and academia to rethink the current paradigm for assessing kidney function to enable dose recommendation in patients with CKD.

Self-reported Race, Serum Creatinine, Cystatin C, and GFR in Children and Young Adults With Pediatric Kidney Diseases: A Report From the Chronic Kidney Disease in Children (CKiD) Study

RATIONALE & OBJECTIVE

Recent reassessment of the use of race in estimated glomerular filtration rate (eGFR) in adults has instigated questions about the role of race in eGFR expressions for children. Little research has examined the associations of self-reported race with measured GFR (mGFR) adjusting for serum creatinine or cystatin C in children and young adults with chronic kidney disease (CKD). This study examined these associations and evaluated the performance of the previously published "U25" (under the age of 25 years) eGFR equations in a large cohort of children and young adults with CKD.

STUDY DESIGN

Observational cohort study.

SETTING & PARTICIPANTS

Participants in the Chronic Kidney Disease in Children (CKiD) study including 190 Black and 675 non-Black participants contributing 473 and 1,897 annual person-visits, respectively.

EXPOSURE

Self- or parental-reported race (Black, non-Black). Adjustment for serum creatinine or cystatin C, body size, and socioeconomic status.

OUTCOME

mGFR based on iohexol clearance.

ANALYTICAL APPROACH

Linear regression with generalized estimating equations, stratified by age (<6, 6-12, 12-18, and ≥18 years) incorporating serum creatinine or serum cystatin C. Contrasting performance in different self-reported racial groups of the U25 eGFR equations.

RESULTS

Self-reported Black race was significantly associated with 12.8% higher mGFR among children in regression models including serum creatinine. Self-reported Black race was significantly associated with 3.5% lower mGFR after adjustment for cystatin C overall but was not significant for those over 12 years. The results were similar after adjustment for body size and socioeconomic factors. The average of creatinine- and cystatin C-based U25 equations was unbiased by self-reported race groups.

LIMITATIONS

Small number of children < 6 years; lean body mass was estimated.

CONCLUSIONS

Differences in the creatinine-mGFR relationship by self-reported race were observed in children and young adults with CKD and were consistent with findings in adults. Smaller and opposite differences were observed for the cystatin C-mGFR relationship, especially in the younger age group. We recommend inclusion of children for future investigations of biomarkers to estimate GFR. Importantly, for GFR estimation among those under 25 years of age, the average of the new U25 creatinine and cystatin C equations without race coefficients yields unbiased estimates of mGFR.

Comparison of Cystatin C and Creatinine-Based Equations with Measured Glomerular Filtration Rate in a Diverse Pediatric Population

BACKGROUND

Accurate assessment of kidney function is essential for early detection of kidney damage. While measured glomerular filtration rate (mGFR) is occasionally used as a reference, estimated GFR (eGFR) from serum creatinine- and cystatin C (CysC)-based equations are routinely used in clinical practice as a reliable and less invasive approach. In pediatric populations, CysC-based equations provide a closer approximation as they are independent of body composition. Limited information is available on the performance of CysC-based equations in comparison with mGFR with tracers other than iohexol. Therefore, the goal of our study was to evaluate how eGFR, based on several CysC- and creatinine-based equations, with and without race correction, relates to mGFR in a diverse pediatric population.

METHODS

A total of 43 patients (7 months to 21 years) from diverse race/ethnicity were retrospectively studied to compare the mGFR from multiple blood sample collections after intravenous tracer injection (Tc-99mDTPA) with eGFR using 9 equations. Deming regression analyses were performed to assess correlation between the mGFR and eGFRs.

RESULTS

The average mGFR for this cohort was 95.0 mL/min/1.73 m2. Race-corrected (RC) equations gave overestimated eGFR across all ethnic groups, with the lowest bias for Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) CysC-creatinine (34.14 mL/min/1.73 m2). The best correlations to mGFR, percentage of eGFR within 30% of mGFR (P30), and lowest biases were from non-race-corrected (NRC) equations Chronic Kidney Disease in Children (CKiD) (0.6460, 65.1%, 2.86 mL/min/1.73 m2), CKD-EPI CysC (0.6858, 69.8%, 11.01 mL/min/1.73 m2), and Schwartz CysC (0.6876, 79.1%, -14.00 mL/min/1.73 m2).

CONCLUSION

Overall, CysC-based equations without race correction provide a good approximation of mGFR and a less invasive alternative to monitoring kidney function in pediatric population, irrespective of race/ethnicity.

The Level of Plasma Cystatin C in Patients with Chronic Kidney Disease

Background: Chronic kidney disease (CKD) is an increasingly common disease worldwide and has become a global health problem, especially in Vietnam. Cystatin C is a marker for the detection, classification, and prognosis of CKD. Cystatin C is filtered entirely through the glomerular membrane, reabsorbed, and metabolized completely in the renal tubules. In case of damage to the kidneys, glomerular filtration rate declines, and some substances increase in the blood, such as cystatin C. The concentration of cystatin C changes with damage to the renal system. Objectives: This study aimed to estimate the concentration of cystatin C and its variation in the different stages of CKD. Methods: A descriptive, cross-sectional study was conducted on 40 healthy individuals and 137 patients with CKD grade III, IV, and V in 103 Hospital. The concentration of cystatin C was estimated in all subjects. Results: Cystatin C plasma levels were significantly higher in the CKD group (9.17 ± 3.75 mg/L) than in the control group (0.82 ± 0.12 mg/L). Cystatin C plasma levels increased linearly with the serious kidney failure as the stage of CKD. Conclusions: Cystatin C is an effective marker for estimating kidney damage in CKD.

Age- and sex-dependent clinical equations to estimate glomerular filtration rates in children and young adults with chronic kidney disease

Using data (2655 observations from 928 participants) from the Chronic Kidney Disease in Children Study, we developed and internally validated new glomerular filtration rate estimating equations for clinical use in children and young adults: two forms of K × [heigh(ht) / serum creatinine(sCr)] and two forms of K × [1 / cystatin C(cysC)]. For each marker, one equation used a sex-dependent K; in the other, K is sex-and age-dependent. Glomerular filtration rate (GFR) was measured directly by plasma iohexol disappearance. The equations using ht⁄sCr had sex-specific constants of 41.8 for males and 37.6 for females. In the age- dependent models, K increased monotonically for children 1-18 years old and was constant for young adults 18-25 years. For males, K ranged from 35.7 for one-year-olds to 50.8 for those 18 and older. For females, the values of K ranged from 33.1 to 41.4. Constant K values for cystatin-C equations were 81.9 for males and 74.9 for females. With age-dependency, K varied non-monotonically with the highest values at age 15 for males (K of 87.2) and 12 years for females (K of 79.9). Use of an age-dependent K with ht/sCr models reduced average bias, notably in young children and young adults; age-dependent cystatin-C models produced similar agreement to using a constant K in children under 18 years, but reduced bias in young adults. These age-dependent proposed equations were evaluated alongside estimated GFRs from 11 other published equations for pediatrics and young adults. Only our proposed equations yielded non- significant bias and within 30% accuracy values greater than 85% in both the pediatric and young adult subpopulations.

GFR Estimation After Cystatin C Reference Material Change

Introduction

Glomerular filtration rate (GFR) is routinely estimated with cystatin C. In June 2010, the International Federation of Clinical Chemistry (IFCC) released a certified cystatin C reference material (ERM-DA471/IFCC), and new cystatin C glomerular filtration rate estimation (eGFR) equations were developed with the IFCC standard. Early in 2018, Siemens discontinued their nonstandardized cystatin C reagent kits and replaced them with IFCC-calibrated kits in the US market. The aim of the current study was to assess the effect of IFCC calibration on cystatin C values and corresponding GFR estimations.

Methods

Cystatin C concentration was measured in 81 pediatric patients using a plasma sample from their nuclear GFR measurement with 99mTc-diethylenetriaminepentaaccetic acid. Calibration curves were generated using Siemens nonstandardized and IFCC-standardized kits to measure paired cystatin C concentrations in each sample. GFR-estimating equations using pre-IFCC and IFCC cystatin C values were compared using Bland-Altman analyses.

Results

The IFCC-standardized assay resulted in a mean increase in the measured cystatin C value of 24%. Estimating equations consistently overestimated GFR prior to IFCC standardization. Following incorporation of the IFCC standard, the Full Age Spectrum equation demonstrated the best overall performance, whereas the Chronic Kidney Disease in Children (CKiD) equation was more accurate in children with decreased GFR.

Conclusion

Incorporation of the IFCC standard significantly increased cystatin C values and affected the performance of GFR estimating equations. Clinical laboratories and providers may need to update the equation used for cystatin C-based estimation of GFR following adoption of the IFCC reference standard.

Cystatin C as a biomarker of chronic kidney disease: latest developments

INTRODUCTION

Chronic kidney disease (CKD) is common, occurring in over 10% of individuals globally, and is increasing in prevalence. The limitations of traditional biomarkers of renal dysfunction, such as serum creatinine, have been well demonstrated in the literature. Therefore, augmenting clinical assessment with newer biomarkers, such as serum cystatin C, has the potential to improve disease monitoring and patient care.

AREAS COVERED

The present paper assesses the utility and limitations of serum cystatin C as a biomarker for CKD in light of the current literature.

EXPERT OPINION

Serum cystatin C has been well established as an early and accurate biomarker of CKD that is particularly helpful in patients for whom creatinine is an inadequate marker or for whom more cumbersome methods of glomerular filtration rate (GFR) measurement are impractical. Current research questions are no longer focused on if, but rather when and how often cystatin C should be used in the evaluation of CKD patients. However, transition of all reagents and estimated GFR equations to the newly established International Standard is critical for developing generalizable data.