Reliability of 51Cr-EDTA plasma and urinary clearance as a measure of residual renal function in dialysis patients

Abstract

Purpose: In dialysis patients, longer survival is associated with a higher residual renal function. Randomized controlled trials are conducted to clarify how residual renal function can be preserved. However, existing methods for measuring residual renal function are uncertain and there is a need for establishing a standard for measurements of glomerular filtration rate (GFR) in dialysis patients. Methods: 51Cr-EDTA clearances in plasma, urine, and dialysate were evaluated in a sample of 12 hemodialysis and 12 peritoneal dialysis patients. The patients’ condition was generally stable, and all patients were investigated twice within 4–10 days. Results: Plasma clearances of 51Cr-EDTA for all patients ranged between 2.1 and 30.8 mL/min/1.73m2, whereas urinary 51Cr-EDTA clearances ranged from 0.7–20.0 mL/min/1.73m2. This difference was statistically significant (p < 0.001). Week-to-week reproducibility expressed as coefficients of variation were below or equal to 10% for plasma clearances and 13% for urinary clearances in hemodialysis patients and 14% in peritoneal dialysis patients. Conclusions: This study demonstrated a difference between 51Cr-EDTA plasma and urinary clearances in dialysis patients. Plasma clearance of 51Cr-EDTA had the best reproducibility. For repeated measurements as in clinical prospective trials, we recommend 51Cr-EDTA plasma clearance based on blood sampling at 5 + 24 hours with subtraction of 51Cr-EDTA dialysate clearance in peritoneal dialysis patients. Further studies are needed to corroborate our findings.