Lancet
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Antineutrophil cytoplasmic antibody (c-ANCA) has a reported sensitivity and specificity greater than 90% for active Wegener's granulomatosis in selected patients with previously-defined disease. Because of these reports, some clinicians believe that a positive c-ANCA result provides strong circumstantial evidence for the diagnosis of Wegener's granulomatosis in patients with compatible clinical symptoms. However, this approach has not been examined prospectively. ⋯ The specificity remained greater than 90% regardless of baseline corticosteroid use or disease activity; however, the sensitivity and positive predictive value remained poor. For Wegener's granulomatosis defined by biopsy criteria and compatible clinical symptoms, the sensitivity was 83% (53%-100%); however, the positive predictive value was 36%. These results raise serious questions about the use of positive c-ANCA tests in diagnosing Wegener's granulomatosis in patients with clinical symptoms alone.