COMPARISON OF FACTOR VIII-RELATED ANTIGEN AND ERYTHROCYTE SEDIMENTATION-RATE IN OUTPATIENT MANAGEMENT OF VASCULITIS

Electroimmunodiffusion (Laurell rocket) determinations of factor VIII- related antigen in plasma were ordered to determine the cost/benefit r atio for factor VIII-related antigen as a putative test for endothelia l damage in suspected vasculitis. Twenty-seven consecutive patients re ferred for vasculitis or suspected vasculitis were identified and foll owed up for an average of 9.1 +/-months (range: one to thirty-three mo nths) in a prospective, unblinded study performed in a clinic, associa ted with a 1054-bed inner-city university hospital. There was no diffe rence in Westergren erythrocyte sedimentation rate (WESR) in patients with final diagnosis of systemic vasculitis (SV) (38 +/-12 mm/hour) co mpared to those without vasculitis (NV) (27 +/-7) as the final diagnos is. The mean plasma concentration of factor VIII-related antigen was s ignificantly elevated in SV (344 +/-100%) when compared with NV (147 /-39%) (P < 0.016). The factor VIII-related antigen test in this study was 2.56 times more likely (crude odds ratio) than the WESR to contri bute to a change in diagnosis or therapy (P=0.016). Positive and negat ive predictive values (PPV and NPV) for factor VIII-related antigen (a bnormal at greater than 220% of the normal value) were both 70%. PPV a nd NPV for WESR were 56% and 86%, respectively. The factor VIII-relate d test was less cost-effective than the WESR in the follow-up period u nless it was important to define complete remission or differentiate v asculitis flare from infection. The authors conclude that factor VIII- related antigen is a useful test in the initial diagnosis of vasculiti s.