Immunostaining for galactose-deficient immunoglobulin A is not specific for primary immunoglobulin A nephropathy.

The pathogenesis of IgA nephropathy is driven by immune complex deposition in the mesangium. These immune complexes contain galactose-deficient IgA1 (gd-IgA1), autoantibodies against gd-IgA1, and other proteins. From a diagnostic point of view, it appears logically that the detection of gd-IgA1 in kidney biopsies should help to establish the diagnosis. The question asked by Cassol et al. was if using the “specific” antibody would add diagnostic value compared to the “non-specific” antibody. Surprisingly, they detected gd-IgA1 not only in cases with primary IgA nephropathy but also in cases with secondary IgA nephropathy or IgA-dominant infection-associated glomerulonephritis. Thus, adding antibodies to gd-IgA1 to routine practice will not bring the diagnostics of IgA nephropathy to a new level.