Health Encyclopedia

C1 esterase inhibitor

Definition

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.

Alternative Names

C1 inhibiting factor; C1-INH

How the test is performed

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.

Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

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.

Normal Values

C1 esterase inhibitor: 16 to 33 milligrams per deciliter (mg/dL)

What abnormal results mean

Abnormal results may be due to certain types of angioedema.

What the risks are

Excessive bleeding
Fainting or feeling light-headed
Hematoma (blood accumulating under the skin)
Infection (a slight risk any time the skin is broken)
Multiple punctures to locate veins

Review Date:5/27/2007
Reviewed By:Steve Lee, DO, Rheumatology Fellow, Loma Linda University Medical Center,Loma Linda, CA. Review provided by VeriMed Healthcare Network.

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