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

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.

Cystatin C as a Marker of Kidney Function in Children

This review examines the reliability of cystatin C as a biomarker for kidney function in paediatric populations. Chronic kidney disease (CKD) affects a significant number of children globally, leading to severe health complications such as anaemia, hypertension, and growth disorders. Traditionally, kidney function has been assessed using the estimated glomerular filtration rate derived from serum creatinine, though this method is flawed due to variability in muscle mass, age, gender, and diet. Cystatin C offers an alternative as it is less influenced by these factors. Evidence from various studies indicates that cystatin C provides a more accurate assessment of kidney function, especially in neonates and children with urinary tract malformations. Additionally, it is more reliable in early detection of acute kidney injury in paediatric intensive care units. Despite its potential, cystatin C is not yet widely adopted in clinical guidelines, primarily due to a lack of large-scale paediatric studies. Nonetheless, existing research supports its utility in providing a consistent and precise measure of kidney function across different paediatric age groups, suggesting that it could enhance early diagnosis and management of CKD in children if more extensive validation studies are conducted.

Evaluation of eGFR methods in a sub-Saharan African community-based pediatric population

BACKGROUND

Accurate assessment of the estimated glomerular filtration rate (eGFR) plays a pivotal role in the early detection, management, and optimal medication dosing for chronic kidney disease (CKD). However, validation of eGFR, utilizing cystatin C-based equations, is limited in African children and adolescents with CKD. We evaluate the agreement of eGFR equations incorporating both cystatin C and creatinine in this specific population.

METHODS

This community-based study assessed CKD in children (2-15 years) using cystatin C and serum creatinine. eGFR agreement with the reference was evaluated with Bland-Altman plots, ROC curves, and Lin's CCC, using the Under-25 serum creatinine-cystatin C equation as the reference standard. Pairwise ROC comparisons assess the statistical differences in estimation equation agreement.

RESULTS

Among 666 children (mean age, 7.8 ± 3.8 years; 48.6% male), CKD prevalence was 11.6% (95% CI, 9.2-14.2%). Notably, the Chehade equation, using combined biomarkers, aligned best with the reference, displaying the lowest mean deviation (- 0.59; 95% CI, - 1.19 to 0.01), superior agreement (P10, 91.0%; P30, 96.70%), and highest discriminatory power (0.989). In contrast, CKD-EPI 2012 cystatin C had the highest mean deviation (- 35.90) and lowest discriminatory power (0.79). Equations combining creatinine and cystatin C (Schwartz, Chehade, Full Age Spectrum) demonstrated strong positive Lin's CCC with CKiD U25 creatinine-cystatin C, while Bouvet showed a notably weak correlation (Lin's CCC, 0.22).

CONCLUSION

In African children with CKD, the Chehade, CKiD Under 25 creatinine-based equations, and the Full Age Spectrum equations show promise for CKD diagnosis. However, a measured GFR is essential to identifying the most accurate eGFR equation in this population.

Understanding Similarities and Differences in CKD and Dialysis Care in Children and Adults

In lower-income settings there is often a dearth of resources and nephrologists, especially pediatric nephrologists, and individual physicians often find themselves caring for patients with chronic kidney diseases and end-stage kidney failure across the age spectrum. The management of such patients in high-income settings is relatively protocolized and permits high-volume services to run efficiently. The basic principles of managing chronic kidney disease and providing dialysis are similar for adults and children, however, given the differences in body size, causes of kidney failure, nutrition, and growth between children and adults with kidney diseases, nephrologists must understand the relevance of these differences, and have an approach to providing quality and safe dialysis to each group. Prevention, early diagnosis, and early intervention with simple therapeutic and lifestyle interventions are achievable goals to manage symptoms, complications, and reduce progression, or avoid kidney failure in children and adults. These strategies currently are easier to implement in higher-resource settings with robust health systems. In many low-resource settings, kidney diseases are only first diagnosed at end stage, and resources to pay out of pocket for appropriate care are lacking. Many barriers therefore exist in these settings, where specialist nephrology personnel may be least accessible. To improve management of patients at all ages, we highlight differences and similarities, and provide practical guidance on the management of children and adults with chronic kidney disease and kidney failure. It is important that children are managed with a view to optimizing growth and well-being and maximizing future options (eg, maintaining vein health and optimizing cardiovascular risk), and that adults are managed with attention paid to quality of life and optimization of physical health.