Complement component 3 (C3)


Complement C3 is a blood test that measures the activity of a certain protein. This protein is part 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.

The complement system protects the body from infections, dead cells and from foreign material. Rarely, people may inherit deficiency of some complement proteins. These people are prone to certain infections or autoimmune disorders.

There are nine major complement proteins. They are labeled C1 through C9. This test measures C3.

Blood test

Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. Preparation may vary depending on the specific test.

How the Test is Performed

How to Prepare for the Test

How the Test will Feel

Why the Test is Performed

Normal Results

What Abnormal Results Mean