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
For external users, separate and freeze immediately. Transport frozen