Protein S and C antigen levels in proteinuric patients: dependence on type of glomerular pathology

The cause of the thrombotic tendency in nephrotic patients is unknown. Recent reports of thrombotic complications in patients with deficiencies of protein C or protein S (natural inhibitors of coagulation) have raised the possibility that decreased levels of these proteins may play a role in the hypercoagulable state of nephrotic patients. We measured the levels of protein C, total protein S, and free protein S antigens in 42 patients (21 nephrotic and 21 non-nephrotic) with one of four types of glomerular pathology: diabetic nephropathy (DM), focal glomerular sclerosis (FGS), membranous glomerulonephritis (MGN), and chronic renal failure due to hypertension (CRF). Protein C and total protein S antigen levels were significantly higher in FGS and MGN than they were in DM or CRF. Free protein S levels were lower in DM than they were in MGN. Protein C, total protein S, and free protein S levels did not significantly correlate with either serum albumin or degree of proteinuria. The mean levels of the three proteins did not differ between nephrotic and non-nephrotic patients. Free protein S and protein C were, however, significantly correlated (P less than .005 and P less than .002, respectively) with the type of glomerular pathology, independent of differences in age, sex, serum albumin, or degree of proteinuria. These data suggest that abnormalities of free protein S and protein C are related to the nature of the underlying renal disease, rather than to the degree of proteinuria.