Measurement of serum IgA and C3 may predict the diagnosis of patients with IgA nephropathy prior to renal biopsy.

The levels of serum IgA and C3 in patients with IgA nephropathy were determined using international standard serum (IFCC/CRM470) in a multicenter trial in Japan. The ratio of serum IgA to C3 (serum IgA/C3 ratio) without any information from renal biopsy was used for the diagnosis of IgA nephropathy. Three hundred and six patients with IgA nephropathy and other glomerular diseases, and 418 healthy adults were examined. The new diagnostic standardized criterion in patients with IgA nephropathy, obtained by nephelometric immune assay based on the international reference preparation CRM470, was 315 mg/dl. The serum IgA/C3 ratio was a more useful marker for distinguishing IgA nephropathy from non-IgA nephropathy together with serum IgA levels. This suggests that the measurement of serum IgA and C3 may predict the diagnosis of patients with IgA nephropathy prior to renal biopsy. Copyright 2000 Wiley-Liss, Inc.