IgA antineutrophil cytoplasmic antibody in Henoch-Schönlein purpura.

Sera from 29 children with acute Henoch-Schönlein purpura were tested for IgA antineutrophil cytoplasmic antibody (ANCA) and for IgA rheumatoid factor (RF). All sera were negative for IgA ANCA by indirect immunofluorescence, but 13 of 29 patients had weakly positive results for IgA ANCA when tested using an enzyme immunoassay. Sixteen of 29 children were IgA RF seropositive. IgA RF seropositive patients had significantly higher titers of IgA ANCA as compared with IgA RF seronegative patients (p = 0.0002). Indeed, of the 16 patients who were IgA RF seropositive, 13 also had positive tests for IgA ANCA, while none of the IgA RF seronegative patients had positive tests for IgA ANCA (p = 0.00001). Removal of IgA RF from eight sera by adsorption with immobilized IgG produced comparable reductions in the titers of both IgA RF and IgA ANCA. We conclude that IgA ANCA is not an important serologic marker in Henoch-Schönlein purpura, but the presence of serum IgA RF may produce weak false-positive results for IgA ANCA in some patients.