Use of Likelihood Ratios Can Improve the Clinical Usefulness of Enzyme Immunoassays for the Diagnosis of Small-Vessel Vasculitis

Abstract

Antineutrophil cytoplasmic antibodies (ANCAs)1 are associated with small-vessel vasculitis (SVV), such as Wegener granulomatosis, microscopic polyangiitis, and Churg–Strauss syndrome (1). Indirect immunofluorescence (IIF) analyses can distinguish 2 major patterns: cytoplasmic and perinuclear. The cytoplasmic ANCA pattern is typically associated with antibodies to proteinase 3 (PR3), whereas the perinuclear ANCA pattern is typically associated with antibodies to myeloperoxidase (MPO). PR3 ANCAs are predominantly seen in patients with Wegener granulomatosis, whereas MPO ANCAs are predominantly seen in patients with microscopic polyangiitis(1)(2)(3). Studies that have addressed the clinical usefulness of specific enzyme immunoassays (EIAs) for PR3 and MPO for the diagnosis of SVV have used a single cutoff value. In this letter, we illustrate how the likelihood ratio (LR) for SVV depends on the titer of anti-PR3 or anti-MPO antibodies. Our calculations are based on a clinically well-defined group of 37 consecutive patients with newly diagnosed SVV (data collected over a 10-year period) and 285 consecutive control individuals with disease (data collected over 21 months) that a physician suspected to be a …