A deficiency in a complement component can often be narrowed down by comparing the CH50 (total hemolytic complement activity) and AH50 (total alternative pathway activity).
Classical Pathway Components: C1, C2, C4
Terminal Components: C3, C5, C6, C7, C8, C9
Alternative Pathway Components: Factor B, Factor D, Properdin
CH50 in U/mL
AH50 in U/mL
Possible Deficiency
0
0
C3, C5, C6, C7, C8
0
normal
C1q, C1r, C1s, C2, C4
normal
0
Factor B, Factor D, Properdin
low
low
C9, Factor H, Factor I, in vivo activation, heterozygous complement deficiency in C3, C5, C6, C7, and C8
where:
• A CH50 or AH50 of 0 indicates a complete deficiency in the affected complement component.
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