C1 Inhibitor Level


C1 Inhibitor Level

Site(s) or Laboratory offering Test/Investigation

Referral laboratory



Also Known as/Frequency of Test

C1EQ; C1 Esterase Inhibitor, C1 Esterase Antibodies


C1 esterase inhibitor deficiency is the most common complement deficiency resulting in hereditary angioedema. 85% of HAE results from a reduced level of the C1Inhibitor. Acquired C1 inhibitor deficiency may occur with B-cell lymphomas and some autoimmune diseases. Samples collected during an acute attack of angioedema due to C1 inhibitor deficiency are characterised by a low C4. A normal C4 level virtually excludes all forms of C1 inhibitor deficiency. Referred outside of EPA.


Referred outside of EPA

Sample type


Turnaround times (TAT) Urgent/Routine/GP or OPD

2 weeks

Reference intervals (adult unless stated)

0.19 – 0.39 g/L