C1 esterase inhibitor (C1-INH) is a protein found in the fluid part of your blood that controls C1, the first component of the complement system. The complement system is a group of proteins that move freely through your bloodstream. The proteins work with your immune system and play a role in the development of inflammation. There are nine major complement proteins. They are labeled C1 through C9.
This article discusses the test that is done to measures the amount of C1-INH in your blood.
C1 inhibiting factor; C1-INH
How the test is performed
A blood sample is needed. This is usually taken through a vein. The procedure is called a venipuncture.
How to prepare for the test
No special preparation is needed.
How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performed
Your doctor may order this test if you have signs of hereditary angioedema. Hereditary angioedema is caused by low levels of C1-INH.
C1 esterase inhibitor: 16 to 33 milligrams per deciliter (mg/dL).
Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.
What abnormal results mean
Abnormal results may be due to certain types of angioedema.
What the risks are
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining blood from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
Fainting or feeling light-headed
Hematoma (blood accumulating under the skin)
Infection (a slight risk any time the skin is broken)
Introduction to the Complement System. In: Adkinson NF Jr, ed. Middleton’s Allergy: Principles and Practice. 7th ed. Philadelphia, Pa: Mosby Elsevier; 2008:chap 6.
Ariel D. Teitel, MD, MBA, Clinical Associate Professor of Medicine, NYU Langone Medical Center. Review provided by VeriMed Healthcare Network. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, Bethanne Black, Stephanie Slon, and Nissi Wang.