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Complement Factor H and Factor I

Category Immunology
Test background

Factor H and I are regulators of the complement cascade. Factor H is a co-factor for factor I mediated cleavage of alternative pathway C3b into iC3b and it competes with factor B to prevent formation of the alternative pathway C3 convertase.

Dysregulated alternative pathway regulation is a cause of dense deposit disease (DDD) and can be caused by C3 nephritic factors, anti-Factor H antibodies and genetic loss of function mutations of Factor H. Factor H deficiency may also cause atypical haemolytic uremic syndrome (aHUS).

Clinical Indications

C3 glomerulopathy (DDD, C3GN)

Reference range

Factor H = >0.43 g/L
Factor I = >21 mg/L
Ranges verified by reference laboratory

Normal values do not exclude genetic mutations in Factor H & I

Sample & container required Serum (RST rust top)
Sample volume 5-10 mL blood (1 mL serum)
Turnaround time 28 days

Not currently performed in house. This test is performed by radial immunodiffusion at Royal Victoria Hospital, Newcastle