Extracellular fluid volume (ECV) distribution across glomerular filtration rate (GFR) categories in a representative adult population: A Cr-51-EDTA plasma clearance study

2031 Objectives GFR is essential in chronic kidney disease (CKD) diagnosis and stratification and exogenous tracer plasma clearance is the gold standard for its precise assessment. Assuming a 2-compartment model, sequential plasma sampling biexponentially approximated allows for simultaneous GFR and ECV calculation. In CKD, ECV is both clinically relevant and meaningful for GFR indexing. However, ECV can be altered by both CKD and treatment. We aim to describe ECV distribution across a wide GFR range in adults. Methods GFR was measured in 278 pts (58.6±15.2 yrs) for clinical purposes, after i.v. injection of Cr-51-EDTA and collection of 10 blood samples at 5 min - 4 hours p.i.. GFR (ml/min) and ECV (l) were calculated as well as, after body surface area (BSA) indexation, GFR/BSA (ml/min/1.73 m2) and ECV/BSA (l/1.73 m2). According to GFR/BSA, patients were allocated in groups A (≥ 90), B (89-30) and C ( Results GFR/BSA ranged from 5.1 to 161.5. ECV varied independently of GFR (r2 = 0.00). ECV (ECV/BSA) was 15.2±2.7 (13.7±2.0), 14.9±3.2 (13.4±2.1) and 16.8±4.2 (14.9±2.5) for groups A, B and C respectively. Significant differences between all group pairs were found for age, GFR and GFR/BSA. BSA was non-different for all group pairs. ECV and ECV/BSA did not differ between groups A and B but was significantly higher in group C compared to both A and B groups. Conclusions ECV varies independently of GFR through the entire range of the later. Slightly higher (≈1.5 l/1.73 m2) ECV/BSA is observed in only those patients with severely reduced kidney function or renal failure. It is concluded that despite the considerable heterogeneity of patients submitted to GFR measurement, ECV can be reasonably adopted for GFR indexation.