Reclassification of membranoproliferative glomerulonephritis: Identification of a new GN: C3GN

Table 2 Complement testing in patients with C3 glomerulopathy

Test	Interpretation	Limitations
C3 and C4 levels	C3 frequently depressed and support diagnosis; Normal C4 suggests an alternative pathway process	Non-specific
Soluble C5b-9	May be indicator of active disease; May identify patients who will benefit from C5 blockade	Test not widely available
C3 nephritic factor	Associated with C3 glomerulopathy; May identify patients who will benefit from B cell targeted therapies	Levels do not correlate with disease activity; also seen in MPGN type I
Factor H protein levels	May identify underlying mechanism of alternative pathway activity; May identify patients who will benefit from plasma infusion/exchange
Autoantibodies to factor H and factor B	May identify underlying mechanism of alternative pathway activity; May identify patients who will benefit from B cell targeted therapies	Test not widely available
Genetic mutation screening Factor H CFHR1, 2, and 5 Factor I C3 Factor B	May identify underlying mechanism of alternative pathway activity	Not widely available; Clinical implications unknown

MPGN: Membranoproliferative glomerulonephritis; CFHR: Complement factor H related proteins.