Total plasma clearance versus urinary plasma clearance of 51Cr-EDTA in patients with cirrhosis with and without fluid retention

Background and aim. In patients with fluid retention, the total plasma clearance of Cr-51-EDTA (Cl-P) may overestimate the glomerular filtration rate (GFR). The present study was therefore undertaken in order to compare Cl-P with the urinary plasma clearance of Cr-51-EDTA (Cl-U) in patients with cirrhosis with and without fluid retention. Material and methods. A total of 136 patients with cirrhosis (24 without fluid retention, 112 with ascites) received a quantitative intravenous injection of Cr-51-EDTA followed by plasma and quantitative urinary samples for 5 hours. Cl-P was determined from the injected dose relative to the plasma concentration-time area, extrapolated to infinity. Cl-U was determined as urinary excretion relative to the plasma concentration-time area up to voiding. Results. In patients without fluid retention, the difference between Cl-P and Cl-U (Cl-P - Cl-U = Cl-Delta) was mean 4.5 mL/min/1.73 m(2). In patients with ascites, Cl-Delta was significantly higher (17.6 mL/min/1.73 m(2), p < 0.0001). Cl-Delta increased with lower values of GFR (r= 0.458, p<0.001). Repeated measurements of Cl-U in a subgroup of patients with fluid retention (n - 25) gave almost identical values. Different types of corrections of one-pool clearance were almost identical with Cl-P, except for higher clearance values, which were somewhat underestimated by the former. Conclusion. In patients with fluid retention and ascites Cl-P and corrected one-pool clearance overestimates GFR substantially. Although Cl-U may underestimate GFR slightly, patients with ascites should collect urine quantitatively in order to obtain a reliable measurement of GFR.