Pathology Handbook

C1 Esterase Inhibitor



Clinical Indications

Diagnosis of hereditary angioedema (HAE). C1 esterase inhibitor deficiency is the commonest of the inherited complement deficiencies (approx. 1:50,000) and is autosomal dominant. Several members of a family are usually affected.

Test Includes

Functional C1 esterase inhibitor, C3 and C4 levels.

Request Form

Request on ICE


Analysed by referral laboratory if specific criteria met.

Specific Criteria

Investigation of hereditary angioedema. Usually C1 esterase inhibitor analysis will only be undertaken C4 levels are low with normal C3 levels.
The request form should show:

  • Site, duration, frequency and clinical nature of attacks
  • Details of relatives similarly affected

The sample WILL NOT be analysed if insufficient clinical information is provided or if the clinical details provided suggest an inappropriate request.  Samples not analysed will be stored for 1 month and the laboratory must be contacted if there is a specific reason for requiring the test.

Turnaround Time

2 weeks




2 ml


Vacutainer gold top

Lab Handling

Sent to referral lab (Barts & Royal London)

Causes for Rejection

Unlabelled or incorrectly labelled sample; not meeting specific criteria for analysis; inadequate clinical information.

Reference Range

Adult: 0.15 - 0.35 g/L