Antithrombin III loss in patients with nephrotic syndrome or receiving continuous ambulatory peritoneal dialysis. Evidence of inactive antithrombin III in urine of patients with nephrotic syndrome.

Antithrombin III (AT III) was measured as antigen (Ag) and as heparin cofactor (HC) in plasma and urine or dialysate from nine patients with nephrotic syndrome and nine patients receiving continuous ambulatory peritoneal dialysis (CAPD), respectively. Crossed immunoelectrophoresis on heparin-agarose (H-CIE) and crossed immunoelectrofocusing (CIEF) runs were carried out on plasma and urine or dialysate samples. AT III plasma levels of the patients receiving CAPD were in the normal range, whereas levels in the patients with nephrotic syndrome showed a significant reduction. Nevertheless the AT III Ag daily loss was the same in both patient groups, so that an additional AT III loss caused by renal metabolism was suggested in patients with nephrotic syndrome. No alteration in the isoantithrombin plasma distribution was found in any patient. The AT III recovered in urine was almost all inactive, as demonstrated by the quantitative assays and by the H-CIE runs; on the contrary, the findings obtained by functional assays, H-CIE, and CIEF runs on dialysate samples failed to demonstrate any major alteration in the AT III molecule. In urine the AT III CIEF pattern displayed a more acid distribution (pH 4.9 to 4.5) in respect to the plasma AT III (pH 5.2 to 4.6); this pattern was suggested to be related to the renal AT III functional inactivation, whose exact mechanism remains to be clarified.