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

Abstract

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.

Keywords: glomerular filtration rate; growth; pediatrics; renal transplant.

FIGURE 1

Panel (A) Bland–Altman plots of absolute measured GFR and BSA‐indexed measured GFR when the height difference between subsequent GFR measurements is A1 < 5%, A2 5%–14.9%, A3 > 15%. The mean bias and the standard deviation (SD) bias are represented below the graphs. Panel (B) correlation analysis between absolute measured GFR and BSA‐indexed measured GFR when the height difference between subsequent GFR measurements is B1 < 5%, B2 5%–14.9%, B3 > 15%.

FIGURE 2

Panel (A) Bland–Altman plots of absolute measured GFR and CKiDSCr equation based on estimated GFR when the height difference between subsequent GFR measurements is A1 < 5%, A2 5%–14.9%, A3 > 15%. The mean bias and the standard deviation (SD) bias are represented below the graphs. Panel (B) correlation analysis between absolute measured GFR and CKiDSCr equation‐based estimated GFR when the height difference between subsequent GFR measurements is B1 < 5%, B2 5%–14.9%, B3 > 15%.

FIGURE 3

Panel (A) Bland–Altman plots of absolute measured GFR and BSA‐indexed measured GFR when the body surface area difference between subsequent GFR measurements is A1 < 5%, A2 5%–14.9%, A3 > 15%. The mean bias and the standard deviation (SD) bias are represented below the graphs. Panel (B) correlation analysis between absolute measured GFR and BSA‐indexed measured GFR when the body surface area difference between subsequent GFR measurements is B1 < 5%, B2 5%–14.9%, B3 > 15%.

FIGURE 4

Panel (A) Bland–Altman plots of absolute measured GFR and CKiDSCr equation based on estimated GFR when the body surface area difference between subsequent GFR measurements is A1 < 5%, A2 5%–14.9%, A3 > 15%. The mean bias and the standard deviation (SD) bias are represented below the graphs. Panel (B) correlation analysis between absolute measured GFR and CKiDSCr equation‐based estimated GFR when the body surface area difference between subsequent GFR measurements is B1 < 5%, B2 5%–14.9%, B3 > 15%.