Plasma oxalate and creatinine and oxalate/creatinine clearance ratios in normal subjects and in primary hyperoxaluria. Evidence for renal hyperoxaluria.

Plasma oxalate and creatinine were measured repeatedly in healthy individuals and in 12 patients with type 1 primary hyperoxaluria unresponsive to pyridoxine. The mean ratios were 0.025 (SD 0.006) and 0.120 (SD 0.048), respectively. One patient repeatedly had normal plasma oxalate despite markedly raised urinary oxalate and it seems unlikely that this excess oxalate could have come from the liver. Oxalate/creatinine clearance ratios in the normal group had an overall mean of 0.59 (SD 0.27) in 24 h urine collections and 0.741 (SD 0.297) in repeated short clearance periods. Both renal tubular absorption and secretion of oxalate apparently occurred on different days, but this did not depend upon urinary flow rate. Oxalate/creatinine clearance ratios in type 1 primary hyperoxaluria had a mean of 2.88 (SD 3.11). The raised oxalate/creatinine clearance ratios in the patients were not correlated with either plasma oxalate or creatinine. A few patients showed much higher clearance ratios and in some were sufficiently high to indicate that oxalate was generated and secreted in the kidneys.