Carcinoembryonic antigen (CEA) is a protein normally found in the tissue of a developing baby in the womb. Blood levels of this protein disappear or become very low after birth. In adults, an abnormal amount of CEA may be a sign of cancer.

A blood test can be done to measure the amount of CEA in your blood.

Your doctor may order this test if you have signs of certain cancers. For example, levels of CEA in your blood may increase if you have colon cancer. However, this test is not an accurate way to diagnose any type of cancer, and high levels can be found in people without cancer.

This test's most accurate and important use is to see how well a person responds to cancer treatment.

Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic. An elastic band is placed around the upper arm to apply pressure and cause the vein to swell 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.

In infants or young children, the area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if there is any bleeding.

Smoking may increase CEA levels. If you smoke, your doctor may tell you to avoid doing so for a short time before the test.

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.

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample may be more difficult from some people than from others.