Abstract
Objective
To determine the prevalence of antineutrophil cytoplasmic antibodies (ANCA) in patients with diseases that may mimic systemic vasculitides, such as severe multiorgan dysfunction (MOD) and parenchymal pulmonary disorders.
Methods
We conducted a prospective study of patients with MOD admitted to the medical intensive care unit and patients with various lung diseases seen at the outpatient pulmonary clinic of a tertiary care hospital. Patients with a documented diagnosis of Wegener's granulomatosis (WG) served as positive controls. ANCA were determined in serum samples from each patient by a combination of indirect immunofluorescence (IIF) and enzyme‐linked immunosorbent assays (ELISAs) for antibodies to proteinase‐3 and myeloperoxidase (anti‐MPO).
Results
Ninety‐nine patients with MOD, 29 outpatients with various lung disorders, and 18 patients with WG were included in the study. ANCA were detected by IIF alone in 16% (15/96) of patients with nonvasculitic MOD and 17% (5/29) of outpatients with various pulmonary disorders. The majority of the positive IIF specimens from each group displayed an atypical IIF pattern (73% and 80%, respectively). Only 1 specimen from patients with nonvasculitic disorders was positive for anti‐MPO. ANCA by both IIF and ELISA were detected in 78% (12/14) of control patients with WG.
Conclusion
Detection of ANCA by the combination of IIF and antigen‐specific assays for proteinase 3 and myeloperoxidase in diseases that mimic systemic vasculitides is highly specific for WG, microscopic polyangiitis, and Churg‐Strauss syndrome.