391-P: Normalizing Glomerular Filtration Rate (GFR) Using Extracellular Volume (ECV) Instead of Body Surface Area (BSA) : Results from an Analysis of the Preventing Early Renal Loss (PERL) Trial

Standardization of GFR by BSA can underestimate kidney function in overweight individuals. Standardization of GFR by ECV, rather than BSA, may be a way to avoid measurement bias. Our aim was to compare the distribution and agreement of GFR measures in people with type 1 diabetes at risk of kidney disease, and to determine associations with clinical hemodynamic measures. In this exploratory analysis of the PERL clinical trial of allopurinol, the distribution and agreement of 4 measurements for GFR were compared in 542 participants with eligible data. GFR was measured using gold-standard iohexol plasma clearance procedures, and ECV was calculated using the Jødal-Bröchner-Mortensen method, which estimates ECV using results from clearance studies. GFR was standardized using ECV corrected for 14 L of fluid volume rather than 1.73 m2 of BSA. Agreement between measurements was assessed by Bland-Altman and Spearman correlation analyses. The trial primary outcome was re-analyzed using ECV-adjusted GFR. Mean age and BMI were 51±years and 29.5±6.0 kg/m2. The distribution of normalized GFR measures overlapped and agreement was strong; GFR/ECV overestimated GFR/BSA by 2.9 numerical units (mean 70.5 ml/min/14 L vs. 67.6 ml/min/1.73 m2) . Heart rate was associated with unstandardized GFR (r=-0.10, p=0.023) . Associations between diastolic blood pressure and all measures of GFR were observed (r ranged from 0.17-0.18; p-values