THE VALUE OF COMPLEMENT ACTIVATION PRODUCTS IN THE ASSESSMENT OF SYSTEMIC LUPUS-ERYTHEMATOSUS FLARES

Complement activation products (CAP) have been reported as sensitive m arkers of disease activity in systemic lupus erythematosus (SLE). We h ave measured seven parameters of the complement system (C3, C4, factor B, C3a, C4a, iC3b, and the terminal complement complex -TCC-) in 61 S LE patients to study their interrelationship and relative efficacy as diagnostic indicators of lupus activity. Disease activity was judged a ccording to a clinical index (SLEDAI) to be active in 22 and inactive in 39 patients. Subjects with active SLE showed increased levels of C3 a, C4a, and TCC compared with those of stable lupus and normal control s, and plasma concentrations of these CAP manifested a positive correl ation with disease activity scores. However, values of factor B and iC 3b did not correlate with lupus flares. Serum C3 levels were a better reflection of the degree of SLE activity than were C4 levels. The anap hylatoxins were extremely sensitive markers of disease activity but th ey lacked enough specificity, and iC3b was not at all informative for this purpose. On the whole, TCC concentration was the most useful para meter (77% sensitivity, 80% specificity) to monitor lupus activity, co rrelating the best with the activity scoring system, and thus offers a better laboratory marker of lupus severity than conventional measurem ents of complement. (C) 1995 Academic Press, Inc.