1. We have measured the plasma oxalate concentration (POx), urinary oxalate excretion (UOx), oxalate equilibrium distribution volume (ODV), oxalate metabolic pool size [(ODV) × (POx)], total plasma oxalate clearance (PCOx), renal (or dialyser) oxalate clearance (RCOx), non-renal oxalate clearance (NRCOx) and the tissue oxalate accretion rate (TOA)= [(NRCOx) × (POx)] in three patients with severe renal failure due to primary hyperoxaluria who were being treated by peritoneal dialysis or haemodialysis, or by renal transplantation. The clearance (either GFR or dialyser) of [99mTc]diethylenetriaminepenta-acetate (DTPA) and the extracellular fluid volume (ECF) measured as [99mTc]DTPA distribution volume were also determined.

2. Negligible amounts of 14C were found in faeces or as 14CO2 in expired air and hence (NRCOx) = (PCOx-RCOx).

3. Haemodialysis removed oxalate more efficiently than peritoneal dialysis in the patient where a direct comparison was possible. Neither treatment could keep up with the TOA when performed for clinically acceptable times.

4. The plasma oxalate concentrations calculated from 14C clearance through the dialyser and the chemically determined concentration of the oxalate in the dialysate were in the range 111–146 μmol/l. This is higher than in normals and in hyperoxaluric patients who are not in renal failure. Hence, although the ODV and ECF are similar to those of hyperoxaluric patients without renal failure and normal control subjects, the oxalate metabolic pool (ODV × POx) is grossly enlarged.

5. In the patient treated by renal transplantation, the oxalate pool size diminished concurrently with the resumption of oxalate excretion but expanded again as renal function decreased due to oxalosis.

6. The quantitative data show that dialysis procedures can only be a temporary holding operation and the prognosis with transplantation remains bad unless excessive oxalate production can be controlled.

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