C1 Esterase Inhibitor

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This is a test that measures the concentration of an inhibitor of complement in the blood.

C1 inhibiting factor

Blood is drawn from a vein, usually on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

The sample is then sent to the laboratory where the quantity of C1 inhibiting factor is measured.

There are no special preparations.

For a child, it may be helpful to explain how the test will feel, and even practice or demonstrate on a doll. The more familiar your child is with what will happen to them, and the purpose of the test, the less anxiety they 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.

Complement activity (CH50, CH100, terminal complement component, or individual complement proteins) is measured to determine if complement is involved in the development of a number of diseases. Complement activity is also measured to monitor severity of a disease or determine efficiency of treatment.

Patients with hereditary angioedema are often depleted of C1 esterase inhibitor.

Review Date: 04/20/2005
Reviewed By: Stanford Peng, M.D., Ph.D., Division of Rheumatology, Washington University School of Medicine, St. Louis, MO. Review provided by VeriMed Healthcare Network.