The complex of immunoglobulin A and uromodulin as a diagnostic marker for immunoglobulin A nephropathy

Background The only tool to diagnose immunoglobulinn A nephropathy (IgAN) is renal biopsy which requires hospitalization; moreover, renal biopsy has a risk of critical bleeding. Therefore, a non-invasive method for accurate diagnosis of IgAN is desirable and a must-to-have tool for the clinics. For this purpose, we evaluated the diagnostic value of the IgA–uromodulin complex in the urine of patients with IgAN for its feasibility and adequacy. Method We determined the IgA–uromodulin complex as a candidate for a diagnostic marker of IgAN by immunoprecipitation, liquid chromatography−mass spectrometry (LC–MS) and Western blot analysis. The enzyme-linked immunosorbent assay (ELISA) for the IgA–uromodulin complex was developed and applied to urine samples obtained from various kidney disease patients. Result One hundred and three of 126 urine samples (81.7%) from IgAN patients were positive for the IgA–uromodulin complex, while only 25 out of 94 urine samples (26.6%) in other kidney disease patients were positive. Sensitivity was 81.7%, specificity was 73.4%, and diagnosis efficiency was 78.2%. The complex was negative in eight urine samples obtained from patients with Alport syndrome which is almost impossible to discriminate from IgAN by routine urinalysis. Conclusion Detection of the urinary IgA–uromodulin complex by ELISA is a useful non-invasive method to diagnose IgAN.