Diseases & Conditions

AFP - Alpha Fetoprotein


Overview & Description

An alpha fetoprotein, or AFP, test measures the level of the AFP protein. AFP protein is found in everyone's blood. Higher levels are found in the blood of pregnant women, fetuses, and young children. AFP levels can also be elevated in the blood of people with certain diseases and conditions.

AFP can also be measured in the amniotic fluid of a pregnant woman. Amniotic fluid is the substance that surrounds a baby in the womb.

Who is a candidate for the test?

An AFP test is routinely ordered for pregnant women around the 16th week of pregnancy. It is used to screen for the following conditions in the fetus:

  • abnormalities in the urinary tract
  • defects in the abdominal wall, esophagus, or bowel
  • Down syndrome and other chromosomal abnormalities
  • neural tube defects, such as spina bifida
  • The AFP test can also be used to screen for certain cancers. And it can be used to help monitor 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 strong rubber tube, or 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 After the needle is withdrawn, the puncture site is covered for a short time to prevent bleeding.


    Preparation & Expectations

    What is involved in preparation for the test?

    For pregnancy screening, the AFP test is best done during the 16th week of pregnancy. The healthcare provider will estimate the age of the fetus prior to the test.


    Results and Values

    What do the test results mean?

    An elevated AFP level in the blood of a pregnant woman may be caused by a fetal abnormality. However, the AFP is only a screening test. It can show false positive and false negative results. The test can be inaccurate, for example, if the pregnancy dates are wrong. AFP values are also higher if the woman is carrying more than one baby. A fetus 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 an elevated AFP may have further testing. This may include pregnancy ultrasound. Ultrasound is a special X-ray test that uses sound waves to see the baby. The healthcare provider may also recommend an amniocentesis. In this procedure, a needle is inserted into the amniotic fluid through a small hole in the woman's abdomen. This test can further define any problems with the fetus.

    A low AFP level in a pregnant woman may mean that the fetus has Down syndrome. A test called the triple screen can further measure the baby's risk for Down syndrome. The mother's blood is tested for AFP, HCG (the pregnancy hormone), and estriol. These three values are combined in a formula that indicates the probability of the baby having Down syndrome.

    In an adult who is not pregnant, the AFP level is elevated with certain cancers. These include:

  • certain cancers of the liver
  • colorectal cancer
  • ovarian cancer
  • pancreatic cancer
  • testicular cancer
  • If someone has a known cancer that causes increased AFP, the AFP level can be monitored 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. Liver diseases, such as hepatitis, can elevate the AFP level. Bowel inflammations, such as colitis, can cause a higher AFP level.


    Attribution

    Author:Adam Brochert, MD
    Date Written:
    Editor:Crist, Gayle P., MS, BA
    Edit Date:06/30/01
    Reviewer:Carlos Herrera, MD
    Date Reviewed:05/30/01

    Sources

    Laboratory Tests and Diagnostic Procedures, 1993, Chernecky