Plasma oxalate concentration, oxalate clearance and cardiac function in patients receiving haemodialysis.

Pre-dialysis plasma oxalate concentration was measured in a cross-sectional study of 75 patients receiving maintenance haemodialysis. The aims of this study were to enable formulation of hypotheses regarding the determinants of plasma oxalate concentration and to allow preliminary examination of the possibility that hyperoxalaemia confers an increased risk of cardiac and vascular disease even in the absence of primary hyperoxaluria. Plasma oxalate concentration ranged between 7 and 76 mumol/l, mean (SD) 34.6 (18.1) mumol/l (normal range less than 0.8-2.0 mumol/l). Significant correlations were found between plasma oxalate concentration and plasma creatinine, duration of dialysis, current dose of ascorbic acid, and serum phosphate, and each of these variables retained significance on multiple linear regression. Oxalate clearance across a 1 m2 hollow-fibre Cuprophan dialyser, at 500 ml/min dialysate flow and blood flow between 175 and 225 ml/min, was measured 1 h after commencement of dialysis (n = 19). Mean (SD) clearance was 96.5 (27.0) ml/min. No significant association was found between self-reported maximum walking distance or the occurrence of symptoms of cardiac failure and plasma oxalate concentration. No relationship was found between plasma oxalate concentration and electrocardiographic conduction disturbances (n = 8) 'major' ST/T wave changes (n = 22), 'minor' ST/T wave changes (n = 49). Plasma oxalate was significantly greater in patients with radiologically detectable calcification of medium-sized arteries than in those without calcification, but duration of dialysis was also significantly longer in these patients. Routine haemodialysis results in marked hyperoxalaemia, which may be exacerbated by ascorbate supplementation. Oxalate clearance is similar to that of other small molecules such as creatinine and phosphate.(ABSTRACT TRUNCATED AT 250 WORDS)