Specimen

2 mL (0.5 mL min.) serum from 1 SST. Ship refrigerated or frozen. Overnight fasting is preferred.

Usage

C4 is critical to activation of classical pathway. Decreased levels are seen in patients with SLE, Immune Complex disease and Hereditary angioedema. Congenital deficiency of C4 increases the risk of recurrent bacteremia especially S.pneumoniae. This assay is useful in the diagnosis of C4 deficiency and for investigation of a patient with an undetectable Total complement (CH50) level.