C1 esterase inhibitor test
Quick answer: This blood test measures the level of C1 esterase inhibitor, a protein that helps control swelling reactions in the body. Doctors usually order it when you have repeated swelling of the face, throat, hands or gut without hives, to check for hereditary angioedema.
- SampleBlood
- TakesAbout 5 minutes
- Before the testNo special preparation is usually needed.
How the test is done
- 1A nurse confirms whether level, function or both are requested
- 2A vein in your arm is cleaned
- 3A needle draws blood into the right tube
- 4The sample is handled quickly, as this protein can break down
What your results can mean
Reading your report
Ranges and cut-offs differ between labs and methods, so discuss your result with your doctor.
If the result is outside the usual range
A low level can be seen with hereditary angioedema type 1 or acquired angioedema. In type 2 the level can be normal but the protein does not work, so a function test is needed.
Who usually has this test
People with repeated swelling of the face, lips, throat, hands or gut without hives, and their family members.
Risks and aftercare
No special aftercare; seek urgent help for any throat swelling regardless of the result.
Names and options
Also called: C1-INH, C1 inhibitor, hereditary angioedema test
Listed by the hospital as
- C1 ESTERASE INHIBITOR, SERUM
Questions about this test
Is hereditary angioedema the same as an allergy?
No. It is caused by a shortage or faulty form of C1 esterase inhibitor, not by allergy. It usually does not respond to antihistamines in the way allergic swelling does.
Why is C4 often tested at the same time?
C4 is usually low in hereditary angioedema, even between attacks. A low C4 with a low or poorly working C1 inhibitor supports the diagnosis.
Can hereditary angioedema affect pregnancy?
Swelling attacks can change in pregnancy, becoming more or less frequent. Women with this condition are advised to plan pregnancy and birth with a specialist.
Related tests
Tamara Hospital & IVF Centre, Rajajinagar
34/3, 10th Cross Road, opp. Vardhaka Sardar Patel School, 1st N Block, 2nd Stage, Rajajinagar, Bengaluru 560010
The hospital is open 24 hours. Call before you come to check the timing for your scan or sample collection.
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This page explains each test in general terms so you know what to expect. It is not medical advice: your doctor decides which tests you need and what your results mean. Reference ranges differ between laboratories. Updated 4 November 2026.