Alpha-Fetoprotein (AFP) in Blood
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 maternal serum triple or quadruple screening test. Generally done between 15 and 20 weeks, these tests check the levels of three or four substances in a pregnant woman's blood. The triple screen checks alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), and a type of estrogen (unconjugated estriol, or uE3). The quad screen checks these substances and the level of the hormone inhibin A. 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 want you 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's disease, lymphoma, brain tumors, and renal cell cancer.
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Why It Is Done
The AFP test is done to:
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
The health professional drawing blood will:
How It Feels
The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.
You may feel anxious while awaiting results of an alpha-fetoprotein test done to determine the health of your unborn baby.
There is very little chance of a problem from having blood sample taken from a vein.
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 a developing baby (fetus). The amount of AFP in the blood of a pregnant woman can help find certain problems with her baby.
The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, normal values vary with the age of the baby. A high or low AFP may mean that the age of the baby has been recorded wrong or not calculated correctly. An ultrasound may be done to check the baby's age more accurately.
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 giving birth, 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.
In a pregnant woman, a low level of alpha-fetoprotein can mean:
In a nonpregnant adult, alpha-fetoprotein is not normally present.
What Affects the Test
Things that may affect the results of your test include:
What To Think About
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