Comparison of Factor VIII-Related Antigen and Erythrocyte Sedimentation Rate in Outpatient Management of Vasculitis

Abstract

Electroimmunodiffusion (Laurell rocket) determinations of factor VIII-related antigen in plasma were ordered to determine the cost/benefit ratio for factor VIII-related antigen as a putative test for endothelial damage in suspected vasculitis. Twenty-seven consecutive patients referred for vasculitis or suspected vasculitis were identified and followed up for an average of 9.1 ±months (range: one to thirty-three months) in a prospective, unblinded study performed in a clinic, associated with a 1054- bed inner-city university hospital. There was no difference in Westergren erythrocyte sedimentation rate (WESR) in patients with final diagnosis of systemic vasculitis (SV) (38 ± 12 mm/hour) compared to those without vasculitis (NV) (27 ± 7) as the final diagnosis. The mean plasma concentration of factor VIII-related antigen was significantly 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 contribute to a change in diagnosis or therapy (P=0.016). Positive and negative predictive values (PPV and NPV) for factor VIII-related antigen (abnormal at greater than 220% of the normal value) were both 70%. PPV and NPV for WESR were 56% and 86%, respectively. The factor VIII-related test was less cost-effective than the WESR in the follow-up period unless it was important to define complete remission or differentiate vasculitis flare from infection. The authors conclude that factor VIII-related antigen is a useful test in the initial diagnosis of vasculitis.