Detection of anti-neutrophil cytoplasmic antibodies under actual clinical testing conditions.

Anti-neutrophil cytoplasmic antibodies (ANCA) are a useful diagnostic tool for Wegener's granulomatosis (WG) and microscopic polyangiitis (MPA). To maximize diagnostic utility, current guidelines recommend dual testing by standard indirect immunofluorescence (IIF) and target antigen-specific assays. Most published data come from specialized research laboratories, not reflecting the performance of assays under routine clinical conditions. Therefore, we compared the performance of standard IIF, PR3-, and MPO-ANCA-specific direct ELISA, and a PR3-ANCA-specific capture ELISA used alone and in combination under routine clinical conditions. Consecutive serum samples (615) submitted for routine ANCA testing over a 10-month period were assayed. Diagnoses were WG/MPA (n = 86), other autoimmune disease (n = 118), and various others (n = 411). The combination of PR3-ANCA and MPO-ANCA ELISA had the highest sensitivity (72.1%), and C-ANCA determination using IIF, the highest specificity (99.6%). While maintaining maximal diagnostic accuracy, significant labor savings are achieved by screening for WG/MPA by ELISA followed by confirmatory IIF.