The relation between renal histologic features and the presence of circulating
immune complexes was studied in 50 patients with
hematuria. Primary
IgA nephropathy was found in 25 patients, and various other forms of glomerulopathy were seen in the remaining 25 patients. Circulating
immune complexes were detected with the 125I-C1q-binding assay, the
conglutinin-binding assay, and the
anti-IgA inhibition binding assay, the latter detecting specifically
IgA-containing
immune complex-like material. The 125I-C1q-binding assay gave negative findings for all patients except one. With the
conglutinin-binding assay,
immune complexes were found in a similar frequency for patients with and without
IgA nephropathy. However, the
anti-IgA inhibition binding assay gave positive results only in patients with primary
IgA nephropathy (68 percent) and in none of the other patients.
Sucrose density ultracentrifugation, as well as experiments in which the
anti-IgA inhibition binding assay was performed with and without pretreatment of serum with
polyethylene glycol, showed the presumed
IgA immune complexes to have intermediate sedimentation coefficients (11 to 21S). The presence and level of this macromolecular
IgA in the circulation correlated significantly (p less than 0.001) with the presence of
hematuria in patients who had this clinical manifestation intermittently. Furthermore, a significant correlation (r = 0.69, p less than 0.0001) was found between the degree of
hematuria and the degree of positive findings of the
anti-IgA inhibition binding assay. This study shows that in patients presenting with
hematuria, a positive finding on the
anti-IgA inhibition binding assay is restricted to patients with primary
IgA nephropathy and therefore could be of diagnostic value.