Definition This test measures the levels of a protein called alpha-foetoprotein (AFP) in the blood or amniotic fluid. Amniotic fluid is the substance that surrounds a baby in the womb. The function of AFP is not well understood. Unborn and young children produce high amounts of the protein. In adults, the level is usually quite low unless certain diseases are present. For example, AFP levels can be elevated with certain cancers.
Who is a candidate for the test? This test is normally used for one of three reasons. The test can be used to detect certain birth defects in an unborn child, like Down's Syndrome. It can also be used to screen for certain cancers. It can be used to help follow certain cancers that are being treated.
How is the test performed? A blood sample needs to be taken in order to measure the AFP. The blood is usually drawn from a vein in the forearm or the hand. First, the skin over the vein is cleaned with an antiseptic. Next, a tourniquet, is wrapped around the upper arm. This enlarges the veins in the lower arm by restricting blood flow through them. A very thin needle is gently inserted into a vein and the tourniquet is removed. Blood flows from the vein through the needle and is collected into a syringe or vial. The blood sample is sent to the laboratory for testing. After the needle is withdrawn, the puncture site is covered for a short time to prevent bleeding.
What is involved in preparation for the test? No preparation is generally needed for this test. The doctor who orders the test will provide specific instructions if needed.
What do the test results mean? Normal AFP levels depend on the age of the person. Higher levels are normal in young children. Pregnancy also causes a normal increase in the level of AFP.
In an adult who is not pregnant, an elevated AFP can mean different things. As mentioned, this test is normally used to look for or monitor cancer. Certain cancers in the liver, pancreas, bowels, ovaries, and testes may cause increased AFP. If a doctor suspects one of these cancers, a high AFP blood level may indicate the need for other tests to search for cancer.
Alternatively, if someone has a known cancer that causes increased AFP, the AFP level can be followed during treatment. If the AFP level goes down with treatment, the cancer is probably shrinking. If the level goes up, the cancer is probably growing larger.
The AFP level can also be increased by conditions other than cancer. These include a liver disease such as hepatitis, which is an inflammation of the liver, and colitis, an inflammation of the bowel.
A low AFP level is considered normal in an adult who is not pregnant.
In pregnant women, AFP levels are commonly measured when the baby is roughly 15 to 18 weeks old. The test is used to screen for birth defects. Abnormally elevated AFP may indicate foetal defects involving the nervous system, bowels, or heart. High levels may also indicate an inherited condition known as Turner syndrome. Low levels are associated with Down syndrome. However, high AFP levels must be matched with the length of pregnancy. High AFP levels may mean the dates of the pregnancy are wrong. Also, twins or triplets can increase the AFP level. A foetus that is in trouble or has died can also elevate the level of AFP.
Because so many things can increase the level of AFP in pregnancy, a woman who has increased AFP may have further testing. This may include ultrasound. Ultrasound is a special X-ray test that uses sound waves to see the baby. This allows the doctor to see if the birth due dates are wrong, if twins are present, if the baby is alive, and if obvious birth defects are present. Also, the doctor may want to stick a needle through the belly into the womb. This allows the doctor to draw amniotic fluid out of the womb. The AFP level of the fluid can be tested and may give more clues as to the problem.
A low AFP level in a pregnant woman may mean that the foetus has Down syndrome. It may also mean the dates of the pregnancy are wrong. Further testing is often done as with a high AFP.
Author: Adam Brochert, MD Reviewer: eknowhow Medical Review Panel Editor: Dr John Hearne Last Updated: 6/06/2005 Contributors Potential conflict of interest information for reviewers available on request
