To detect an autoantigen and/or an autoantibody which specifically expresses itself before the emergence of initial or clinical symptoms of kidney disorders in a biological sample especially of secondary kidney disorders associated with primary glomerular nephritis and other disorders, on both a method for detecting kidney disorders in an early stage especially secondary kidney disorders associated with primary glomerular nephritis and other disorders, and on a measuring reagent.

In the method and the measuring reagent, an anti-type 4 collagen NC1 antibody or its peptide antibody is detected with an NC1 region of type 4 collagen or its peptide as an antigen (1). In the method and the measuring reagent, type 4 collagen NC1 or its peptide is detected by using an antibody prepare with the type 4 collagen NC1 region or its peptide as an antigen (2).