Antineutrophil cytoplasmic antibodies an update on clinical utility.

Antineutrophil cytoplasmic antibodies (ANCA) are autoantibodies directed against components of neutrophils and monocytes, and are helpful in identifying different forms of vasculitis. Until the discovery of ANCA, there was no specific laboratory method for the investigation of systemic vasculitis. Many issues regarding ANCA, such as their role in the pathogenesis of vasculitis, sensitivity, specificity, predictive value, and antigen specificity are still unclear. The differential diagnosis of the vasculitic syndromes is often difficult because of the variable presentation, but is important because of the variable outcome.Wegener's granulomatosis, microscopic polyangiitis, and Churg-Strauss syndrome are three vasculidities that commonly are associated with a positive ANCA. The "gold standard" for a precise diagnosis of vasculitis depends on both the clinical and pathologic features. ANCA testing is used to support the clinical and pathologic findings. The ANCA pattern, determined by indirect immunofluorescence, can be either cytoplasmic (C-ANCA), perinuclear (P-ANCA), or atypical perinuclear (X-ANCA). Interpretation of the ANCA pattern can be problematic, and a reactive antinuclear antibody can contribute to the confusion, requiring testing for reactivities to specific autoantigens. Proteinase-3 and myeloperoxidase are the most common autoantigens and are commonly associated with C-ANCA and P-ANCA, respectively. ANCA reactivity to other autoantigens is associated with the X-ANCA pattern.