The Creeping Creatinine in a Growing Child With a Kidney Transplant: Distinguishing Progressive Graft Dysfunction From Normal Growth in Pediatric Kidney Transplant Recipients

Background: Pediatric kidney transplant recipients experience creeping creatinine, which is a slow increase in serum creatinine over time. Distinguishing between normal growth-related changes and possible allograft dysfunction becomes challenging when interpreting the increase in serum creatinine. We hypothesized that changes in BSA-indexed measured glomerular filtration rate (mGFR) or creatinine-estimated GFR (eGFR) might not be a true reflection of the renal function post-transplant and that for longitudinal follow-up a stable absolute mGFR is better. Methods: In total, 115 pediatric kidney transplant recipients transplanted between 2000 and 2021, with 319 measured GFR values (each subject had at least 2 values) were enrolled in this retrospective study. We analyzed after stratifying based on the height and BSA changes (< 5% change, 5%–14.9% change, and > 15% change in height and BSA) between measured GFR tests. The agreement between absolute mGFR and both BSA-indexed mGFR or eGFR was analyzed by Bland and Altman analysis and nonparametric Spearman's rank order correlation analysis. Results: The bias between absolute mGFR and either BSA-indexed mGFR or eGFR increased as the % change in height and the BSA increased. Spearman's rank order correlation showed a strong correlation when the BSA and height changes were < 5% and the correlation weakened as the % changes increased. Conclusions: In children who grew more, the BSA-indexed mGFR dropped more than the absolute mGFR. We propose that a stable absolute mGFR can be used to infer stable allograft function in the presence of height growth.