Plasma oxalate concentration and oxalate distribution volume in patients with normal and decreased renal function

In twenty-one patients (sixteen male, five female) with various kidney diseases including primary hyperoxaluria type I (four patients), the plasma oxalate level was calculated from the isotopically determined oxalate clearance and the chemically determined urinary oxalate excretion. The apparent oxalate distribution volume was assessed as well. In patients with impaired kidney function (n = 12), the oxalate clearance was lower and the biological half-life and plasma concentration were higher than in patients with normal kidney function (n = 10). No differences were found in the oxalate-to-creatinine clearance ratio (mean value 1.93), urinary oxalate excretion and apparent oxalate distribution volume. A linear relation was found between the oxalate and creatinine clearance, while the clearance ratio was independent of the degree of renal failure. The apparent oxalate distribution volume was 1.45 times the estimated extracellular fluid volume. Because the isotopically determined plasma oxalate levels are lower than chemically measured ones, a quick and better estimation of plasma oxalate can be made from the urinary oxalate excretion and the creatinine clearance.