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An alpha fetoprotein, (abbreviated as AFP) test measures the level of this protein, which is found in everyone's blood.

Higher levels are found in the blood of pregnant women, unborn infants, and young children. Though AFP levels can be elevated in the blood of people with certain diseases and conditions, this test is normally performed on the blood or the amniotic fluid of a pregnant woman to look for abnormalities in the unborn child. Amniotic fluid is the substance that surrounds a baby in the womb.

Who is a candidate for the test?

An AFP test can be routinely ordered for pregnant women at about the 16th week of pregnancy. It is used to screen for the following conditions in the unborn child:

• abnormalities in the baby's urinary tract
• defects in the baby's abdominal wall, esophagus, or bowel
• Down syndrome and other chromosomal abnormalities
• neural tube defects, such as spina bifida

In adults, the AFP test can be used to screen for certain cancers and monitor them during treatment.

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 After the needle is withdrawn, the puncture site is covered for a short time to prevent bleeding.

For an amniocentesis, the skin of the pregnant woman's abdomen is cleaned with an antiseptic. Then a long, thin needle is inserted into the amniotic fluid through the woman's lower abdomen (usually under ultrasound guidance), and a small amount of fluid is withdrawn into a syringe and sent to the laboratory for testing.

What is involved in preparation for the test?

For pregnancy screening, the AFP test is best done between the 15th and 18th week of pregnancy. A healthcare professional can estimate the duration of pregnancy by the date since the last menstrual period, the size of the uterus, or if necessary, by an ultrasound exam.

What do the test results mean?

An elevated AFP level in the blood of a pregnant woman may be caused by a abnormality in the baby. However, because the AFP is only a screening test, it can be either falsely negative or falsely positive. 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. If the baby is suffering from a serious medical condition or has died, the AFP may be elevated.

Because so many things can increase the level of AFP in pregnancy, a woman who has an elevated AFP in the blood needs further testing. This may include pregnancy ultrasound. Ultrasound is a special test that uses sound waves to see the baby. The healthcare professional may also check the level of AFP in the amniotic fluid by amniocentesis to better define what, if anything, is wrong with the unborn child.

A low AFP level in a pregnant woman may mean that the unborn baby 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. Also, an ultrasound may provide further evidence of Down Syndrome.

• 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 such as hepatitis, bowel inflammation, or colitis.