There is provided a renal disease testing method comprising a complex detection step of detecting a complex of human uromodulin and human IgA in a sample derived from urine collected from a subject. It is preferred that the renal disease testing method of the invention further comprises a determination step of assessing the whether the renal disease is IgA nephropathy based on the ratio of the amount of the complex detected in the complex detection step to the amount of urinary proteins in the sample. The renal disease testing method of the invention has good detection sensitivity and specificity, and can conveniently and safely assess the existence of a renal disease (preferably, IgA nephropathy).