Combination of pediatric and adult formulas yield valid glomerular filtration rate estimates in young adults with a history of pediatric chronic kidney disease

As patients with chronic kidney disease (CKD) transition from pediatric nephrology care to adult care, their kidney function is clinically assessed by estimated glomerular filtration rate (eGFR) using both pediatric and adult equations, which may not be congruent. Here we evaluated commonly used eGFR equations and directly measured iohexol GFR (iGFR) among participants between ages 18 and 26 with a diagnosis of pediatric CKD in the Chronic Kidney Disease in Children (CKiD) cohort. The bedside serum creatinine (SCr)-only equation (CKiD _SCr ), the SCr-only CKD-EPI (CKD-EPI _SCr ), the cystatin C (Cys)-only CKD-EPI (CKD-EPI _Cys ) and the combined SCr and Cys CKD-EPI (CKD-EPI _SCr-Cys ) were compared with a) 279 measured iGFRs obtained from 187 participants and b) 548 eGFRs from the SCr and Cys-based CKiD equation (CKiD _SCr-Cys ) obtained from 219 participants. Among emerging adults with a median iGFR of 49 ml/min/1.73m ² , the CKiD _SCr-Cys equation had low bias (+1.5 ml/min/1.73m ² ) and high correlation (0.94), while CKiD _SCr underestimated iGFR and CKiD _SCr-Cys (–5.6 and –7.4 ml/min/1.73m ² , respectively) and CKD-EPI _SCr had an overestimation bias (+8.2 and +6.1 ml/min/1.73m ² , respectively). However, the CKD-EPI _Cys and CKD-EPI _SCr-Cys exhibited strong agreement with both iGFR and CKiD _SCr-Cys . GFR may also be validly estimated in this population by taking the simple average of CKiD _SCr and CKD-EPI _SCr (average bias +1.3 compared to iGFR and -0.6 compared to CKiD _SCr-Cys ). Clinicians should be aware that individually the pediatric and adult SCr-based estimates of GFR had large discrepancies among emerging adults with pediatric CKD. Thus, when cystatin C is not available, we recommend the average of pediatric and adult SCr-based eGFR as a valid tool for clinical use.