Alpha-Fetoprotein (AFP) Test
An alpha-fetoprotein (AFP) blood test checks the level of AFP in a pregnant woman's blood. AFP is a substance made in the liver of an unborn baby (fetus). The amount of AFP in the blood of a pregnant woman can help see whether the baby may have such problems as spina bifida and anencephaly. An AFP test can also be done as part of a screening test to find other chromosomal problems, such as Down syndrome (trisomy 21) or Edwards syndrome (trisomy 18). An AFP test can help find an omphalocele, a congenital problem in which some of the baby's intestines stick out through the belly wall.
Normally, low levels of AFP can be found in the blood of a pregnant woman. No AFP (or only a very low level) is generally found in the blood of healthy men or healthy, nonpregnant women.
The level of AFP in the blood is used in a serum quadruple screening test. This test is often done between 15 and 22 weeks. It checks the levels of four substances in a pregnant woman's blood. They are the hormone inhibin A, alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), and a type of estrogen (unconjugated estriol, or uE3). The levels of these substances—along with a woman's age and other factors—help the doctor estimate the chance that the baby may have certain problems or birth defects.
Screening tests are used to see what the chance is that your baby has a certain birth defect. If a screening test is positive, it means that your baby is more likely to have that birth defect and your doctor may give you the option to have a diagnostic test to make sure.
Men, nonpregnant women, and children
In men, nonpregnant women, and children, AFP in the blood can mean that certain types of cancer—especially cancer of the testicles, ovaries, stomach, pancreas, or liver—are present. High levels of AFP may also be found in Hodgkin disease, lymphoma, brain tumors, and renal cell cancer.
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Why It Is Done
The AFP test is done to:
- Check the developing baby (fetus) of a pregnant woman for brain or spinal problems (called neural tube defects).
- Check the developing baby (fetus) of a pregnant woman for Down syndrome.
- Find certain cancers, especially cancer of the testicles, ovaries, or liver.
- Check how well treatment for cancer is working.
How To Prepare
You do not need to do anything before you have this test.
If you are pregnant, you will be weighed before the blood test, because the test results will be based on your weight. The test results are also based on race, age, and how many weeks you are in your pregnancy.
How It Is Done
A health professional uses a needle to take a blood sample, usually from the arm.
How It Feels
When a blood sample is taken, you may feel nothing at all from the needle. Or you might feel a quick sting or pinch.
There is very little chance of having a problem from this test. When a blood sample is taken, a small bruise may form at the site.
Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.
In pregnant women, the amount of AFP gradually rises starting in the 14th week of pregnancy. It continues to rise until a month or two before the woman gives birth, and then it slowly decreases. Values are generally slightly higher for black women than they are for white women. Values are slightly lower for Asian women than they are for white women. An accurate estimate of the age of the baby is needed to understand the AFP value correctly.
The normal range of AFP values is adjusted for each woman's age, weight, and race; whether she has diabetes that needs injections of insulin; and the age of her baby (gestational age). If the age of the baby is changed after an ultrasound, the AFP must then be adjusted as well. Each woman and her doctor need to look at the range of AFP values that is normal for her when she has an AFP test.
A normal AFP result does not guarantee a normal pregnancy or healthy baby.
- In a pregnant woman, high alpha-fetoprotein values can mean:
- The age (gestational age) of the baby is wrong.
- The woman is pregnant with more than one baby, such as twins or triplets.
- The baby has a neural tube defect.
- The baby's intestines or other abdominal organs are outside the body (called an abdominal wall defect or omphalocele). Surgery after birth will be needed to correct the problem.
- The baby is not alive.
- In a nonpregnant adult, high alpha-fetoprotein values can mean:
In a pregnant woman, a low level of alpha-fetoprotein can mean:
- The age (gestational age) of the baby is wrong.
- The baby may have Down syndrome.
In a nonpregnant adult, alpha-fetoprotein is not normally present.
AFP test results can be abnormal, even when nothing is wrong with the baby.