Performance of Creatinine-Based and Cystatin C-Based GFR Estimates in Pediatric Hematology-Oncology Patients

Background: Pediatric hematology-oncology (PHO) patients (pts) are at risk for kidney dysfunction from nephrotoxic exposures. Accurate GFR estimation (eGFR) is essential for diagnosis, drug dosing, and prognosis. While adult studies support combined creatinine-cystatin C equations as the most accurate, data in children are limited. We evaluated the performance of creatinine- and cystatin C-based equations against measured GFR (mGFR) in PHO pts. Methods: Of 1301 PHO pts evaluated from Jan 2004 to May 2024, 26 met inclusion criteria: mGFR via iothalamate (n=24) or iohexol (n=2) with standardized serum creatinine and cystatin C measured within 5 days. For pts with multiple mGFRs, only the earliest was used. We excluded cases involving kidney transplant and amputation, and limited analysis to mGFR ≤150 mL/min/1.73 m2. eGFRs were calculated using the CKiD under age 25 (CKiD U25; validated ≥1 year) and European Kidney Function Consortium (EKFC; validated ≥2 years) equations. eGFRs were compared to mGFR using correlation, P10/P30 accuracy, median bias, and RMSE. Confidence intervals used Fisher transformation and binomial exact methods. Results: Median age was 10.3 years; 54% were male; and 85% were white. Diagnoses included solid, hematologic, and neuro-oncologic malignancies, as well as benign hematologic conditions. Most (62%) underwent hematopoietic stem cell transplantation. eGFR performance metrics are shown in Table 1. Differences were modest with overlapping confidence intervals. Among all pts, CKiD U25Avg showed slightly better performance than other CKiD equations. Among patients ≥2 years old, CKiD U25Avg and EKFCcr outperformed cystatin C-only equations. Conclusion: In a diverse PHO cohort, the CKiD U25Avg and EKFCcr methods showed slightly better accuracy in predicting mGFR compared to others. Cystatin C-only equations were more biased and less accurate. Findings support using modern creatinine-based or combined equations for eGFR in PHO pts, though further studies are needed.