Imperial Collage Healthcare

Complement C1 esterase inhibitor – functional


Test Background
Functional C1 inhibitor levels must be requested alongside antigenic C1 inhibitor (see C1 esterase inhibitor – antigenic) and C3 and C4. This test aids diagnosis of type II HAE, affecting 15 % of sufferers. A low C4, plus a normal or raised C1 inhibitor antigenic level, is associated with low/absent C1 inhibitor functional activity. In type I HAE, patients have a low C1 inhibitor antigenic level and low functional activity.


Clinical Indications
Recurrent angioedema, laryngeal oedema, or abdominal pain in the absence of urticaria Family history


Reference Range

0.7-1.3 g/L


Sample Required
Plain tube (Rust; Serum)


Sample Volume
1 mL serum


Transport/Storage

For external users, separate and freeze immediately. Transport frozen

For internal users, transport to I&I ASA


Turnaround Time
21 days


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