Agreement between serum estimates of glomerular filtration rate (GFR) and a reference standard of radioisotopic GFR in children with cancer.

Abstract

Accurate assessment of renal function is important in the care of children with cancer because renal function has implications for anti-tumor medication dosing and eligibility for clinical trials. To characterize agreement between serum estimates of glomerular filtration rate (GFR) and a reference standard of radioisotopic GFR in a large pediatric oncology cohort. We conducted a retrospective cross-sectional study of children who had both radioisotopic GFR (99mTc-diethylenetriaminepentaacetic acid, or 99mTc-DTPA) and serum labs (creatinine, cystatin C) obtained <7days apart between January 2017 and August 2019. We calculated estimated GFR from serum labsusing published equations and calculated agreement using intraclass correlation coefficient (ICC) and Bland-Altman analysis with univariate regression to define predictors of agreement. We included 272 pairs of data. Mean patient age was (mean ± standard deviation) 7.8±5.7years. Mean radioisotopic GFR was 112±33mL/min/1.73m2. Absolute agreement between radioisotopic GFR and serum estimates was only fair (ICC=0.46-0.58) with a mean difference of -26.6 to +0.12mL/min/1.73m2. For radioisotopic GFR measurements <60mL/min/1.73m2, mean differences were greater, with serum estimates overestimating GFR by a mean of 21.5-39.6mL/min/1.73m2. In multivariable modeling, significant predictors of agreement included age, height, acute kidney injury and tumor type. Sensitivity of serum estimates was 14-29% for a GFR <60mL/min/1.73m2. Agreement between radioisotopic GFR and serum estimates of GFR is only fair and serum estimates of GFR have poor sensitivity for clinically relevant GFR <60mL/min/1.73m2. Radioisotopic measurement of GFR likely remains necessary to assess renal function in pediatric oncology patients with decreased renal function.