IgA containing immune complexes and hematuria in ankylosing spondylitis. A prospective longitudinal study.

The occurrence of circulating immune complexes containing IgA (IgA-IC) was studied in groups of patients with ankylosing spondylitis (AS) selected for the presence or absence of hematuria. In studies done with 4 kinds of assays, IgA-IC were found more frequently and in higher titers in the 18 patients with AS with hematuria than in the 40 patients with AS without hematuria. Comparison of clinical indices of disease activity in these patient groups showed that the disease was more active in patients with AS with hematuria. Our findings confirm those made in a previous retrospective study on the relation between hematuria and circulating IgA-IC in AS and suggest that circulating IgA-IC play a role in the pathogenesis of hematuria in AS.