Human pathology
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We studied the histologic findings from extrarenal biopsies (especially of the lung or upper respiratory tract) or autopsies of 68 patients who were tested for serum antineutrophil cytoplasmic antibodies (ANCAs). We used antigen-specific assays to detect antibodies against proteinase 3 (PR3) and myeloperoxidase (MPO), the two types of ANCAs of proven diagnostic value for the spectrum of diseases that includes Wegener's (pathergic) granulomatosis, microscopic polyarteritis (microscopic polyangiitis), Churg-Strauss syndrome, idiopathic necrotizing and crescentic glomerulonephritis, and their variants. Twenty-eight patients had antibodies to PR3 and 16 had antibodies to MPO; no patient had antibodies to both. ⋯ Of six patients with negative tests for ANCAs and histologically diagnosed Wegener's granulomatosis, none had evidence of renal involvement. We conclude that in the appropriate clinical setting the presence of anti-PR3 or anti-MPO antibodies provides reliable evidence of the above spectrum of diseases, but that subclassification (to the extent this is possible) depends on the presence of distinctive clinical or pathologic features. In patients with negative tests for ANCAs, interpretation of clinical and histologic findings remains the only definitive method of diagnosis.