Complement components C3 and C4

Keywords: C3, C4

Specimen:

5mL blood in plain tube.

The specimen should be placed once and transported immediately to the laboratory.

Method:

Immunoassay.

Functional assay if primary deficiency is suspected.

Reference Interval:

C3: 0.9-1.8 g/L

C4: 0.16-0.50 g/L.

Application:

Monitoring activity of immune complex mediated disease eg, SLE, Cryoglobulinaemia.

Detection of primary deficiency of C3 or C4 (rare).

Assessment of angioedema, see also C1 esterase inhibitor.

Interpretation:

Reduced C4 with or without reduced C3: activation by classical pathway (eg, SLE, immune complex disease / Cryoglobulinemia).

Reduced C3 with normal C4: activation by the alternative pathway (eg, sepsis, endotoxin).

Raised C3 and/or C4: acute phase response.

Reduced C4 normal C3 colon C1 inhibitor deficiency

Reference:

Giglas P. In: Rose NR et al eds. Manual of Clinical Laboratory Immunology. 5th ed. ASM Press 1997.

Wen L et al. Journal of Allergy and Clinical Immunology. 2004; 113: 585-93.