Gamma‐variate plasma clearance versus urinary plasma clearance of 51 Cr‐ EDTA in patients with cirrhosis with and without fluid retention

Summary In patients with fluid retention, the plasma clearance of 51 Cr‐ EDTA (Cl exp obtained by multiexponential fit) may overestimate the glomerular filtration rate ( GFR ). The present study was undertaken to compare a gamma‐variate plasma clearance (Cl gv) with the urinary plasma clearance of 51 Cr‐ EDTA (Cl u ) in patients with cirrhosis with and without fluid retention. A total of 81 patients with cirrhosis (22 without fluid retention, 59 with ascites) received a quantitative intravenous injection of 51 Cr‐ EDTA followed by plasma and quantitative urinary samples for 5 h. Cl gv was determined from the injected dose relative to the plasma concentration‐time area, obtained by a gamma‐variate iterative fit. Cl exp and Cl u were determined by standard technique. In patients without fluid retention, Cl gv , Cl exp and Cl u were closely similar. The difference between Cl gv and Cl u (Cl gv – Cl u  = ΔCl) was mean −0·6 ml min −1  1·73 m −2 . In patients with ascites, ΔCl was significantly higher (11·8 ml min −1  1·73 m −2 , P <0·0001), but this value was lower than Cl exp – Cl u (17·5 mL min −1  1·73 m −2 , P <0·01). ΔCl increased with lower values of GFR ( P <0·001). In conclusion, in patients with fluid retention and ascites Cl gv and Cl exp overestimates GFR substantially, but the overestimation is smaller with Cl gv . Although Cl u may underestimate GFR slightly, patients with ascites should collect urine quantitatively to obtain a reliable measurement of GFR .