Role of Cellular Oxalate in Oxalate Clearance of Patients With Calcium Oxalate Monohydrate Stone Formation and Normal Controls

Objectives To examine the cellular, plasma, and urinary oxalate and erythrocyte oxalate flux in patients with calcium oxalate monohydrate (COM) stone formation vs normal controls. Pathologic oxalate clearance in humans is mostly integrated in calcium oxalate stone formation. An underlying cause of deficient oxalate clearance could be defective transmembrane oxalate transport, which, in many tissues, is regulated by an anion exchanger (SLC26). Methods We studied 2 groups: 40 normal controls and 41 patients with COM stone formation. Red blood cells were divided for cellular oxalate measurement and for resuspension in a buffered solution (pH 7.40); 0.1 mmol/L oxalate was added. The supernatant was measured for oxalate immediately and 1 hour after incubation. The plasma and urinary oxalate were analyzed in parallel. Results The mean cellular oxalate concentrations were significantly greater in the normal controls (5.25 ± 0.47 μmol/L) than in those with COM stone formation (2.36 ± 0.28 μmol/L; P < .01). The mean urinary oxalate concentrations were significantly greater in those with COM stone formation (0.31 ± 0.02 mmol/L) than in the controls (0.24 ± 0.02 mmol/L; P < .01). The cellular oxalate concentrations correlated significantly with the plasma ( r = 0.49-0.63; P < .01) and urinary oxalate ( r = −0.29-0.41; P < .03) concentrations in both groups. The plasma oxalate concentrations correlated significantly with the urinary oxalate concentrations ( r = −0.30; P < .03) in the controls and with the erythrocyte oxalate flux ( r = 0.25; P < .05) in those with COM stone formation. Conclusions Our data implicate the presence of a cellular oxalate buffer to stabilize plasma and urinary oxalate concentrations in normal controls.