Hou et al. proposed histological criteria for diagnosis of C3 glomerulopathy (C3G) by mean of immunofluorescence. Using dense deposit disease (membranoproliferative glomerulonephritis type II or DDD) as the gold standard, they defined C3G as dominant C3 staining with intensity at least 2x of immunoglobulins (IgG, IgA, IgM). For example, C3G is diagnosed if C3 2+ and IgG trace but not if IgG 1+. The intensity scale is 0, trace, 1+, 2+, 3+.
The original definition of C3G is C3 positive without Igs was proved to be insensitive. When it was applied in DDD, only 50% of 44 cases were characterized as C3G. DDD was used as the gold standard for C3G because the electron microscopic finding is pathognomonic. Its pathogenesis was a definite alternative complement pathway impairment.
