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.
In some cases a combination of screening tests is done in the first trimester to look for Down syndrome. This combination uses an ultrasound measurement of the thickness of the skin at the back of the fetus's neck (nuchal translucency), plus a blood test of the levels of the pregnancy hormone hCG and a protein called pregnancy-associated plasma protein A (PAPP-A). The combined screenings are about as accurate as the second-trimester maternal serum quad screening.1
Men, nonpregnant women, and children
In men, nonpregnant women, and children, AFP in the blood can mean 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:
- Check the unborn baby of a pregnant woman for brain or spinal problems (called neural tube defects). Such defects occur in about 2 out of every 1,000 pregnancies.2 The chance of a neural tube defect in a baby is not related to the mother's age. Most women whose babies have neural tube defects have no family history of these problems. This test is done between the 15th and 22nd weeks of pregnancy.
- Check the unborn baby of a pregnant woman for Down syndrome. The chance of finding Down syndrome is about 70% when the AFP test is done with the estriol and hCG tests (triple test). The chance of finding Down syndrome increases to about 80% when the hormone inhibin A test is added (quad test).1
- Find certain cancers, especially cancer of the testicles, ovaries, or liver. But up to half of the people with liver cancer do not have high AFP levels.
- Check how well treatment for cancer is working.
- Check for liver cancer (called hepatoma) in people who have cirrhosis or chronic hepatitis B.
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 and how many weeks you are in your pregnancy.
How It Is Done
The health professional drawing blood will:
- Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
- Clean the needle site with alcohol.
- Put the needle into the vein. More than one needle stick may be needed.
- Attach a tube to the needle to fill it with blood.
- Remove the band from your arm when enough blood is collected.
- Put a gauze pad or cotton ball over the needle site as the needle is removed.
- Put pressure on the site and then a bandage.
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.
- You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
- In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
- Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.
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 unborn baby (fetus). The amount of AFP in the blood of a pregnant woman can help find certain problems with her baby.
Normal AFP values may vary from lab to lab. 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.
|Men and nonpregnant women:|
|Women 15–22 weeks pregnant:||
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. The middle of this adjusted range is called the multiple of median (MoM). An AFP value that is 0.5 to 2.5 times the MoM value is considered normal for that woman. 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.
- High alpha-fetoprotein values in a
pregnant woman 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, a high alpha-fetoprotein value 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 has Down syndrome.
In a nonpregnant adult, alpha-fetoprotein is not normally present.
What Affects the Test
Things that may affect the results of your test include:
- If there is more than one baby (fetus). This increases the level of AFP in the blood.
- If you have gestational diabetes.
- If you smoke. This increases the level of AFP in the blood.
- If you had a medical test that used radioactive tracers in the past 2 weeks.
What To Think About
- The level of AFP in the blood is often used in a maternal serum triple or quadruple screening test. Usually 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. For more information see the medical tests Birth Defects Testing, Estrogens, Human Chorionic Gonadotropin (hCG), and Hormone Inhibin A.
- AFP is a screening test to look for possible problems in your unborn baby. Other tests must always be done if the AFP results are abnormal. An ultrasound will likely be done if the AFP is abnormal. If an ultrasound cannot find the cause of the abnormal AFP, an amniocentesis may be recommended. For more information, see the medical tests Fetal Ultrasound or Amniocentesis.
- A normal AFP result does not guarantee a normal pregnancy or healthy baby.
- The amount of AFP in the amniotic fluid may also be measured using amniocentesis. Most women have normal AFP levels in the amniotic fluid, even though the levels may be abnormal in their blood. These women are at low risk of having a fetus with a neural tube defect. For more information, see the medical test Amniocentesis.
- If abnormal levels of AFP are found, talk with your doctor or a genetic counselor. AFP test results can be abnormal, even when nothing is wrong with the baby.
- In people with liver cancer or other types of cancer, a decrease in AFP may mean treatment is working.
- American College of Obstetricians and Gynecologists (2007). Screening for fetal chromosomal abnormalities. ACOG Practice Bulletin No. 77. Obstetrics and Gynecology, 109(1): 217–227.
- American College of Obstetricians and Gynecologists (2003). Neural tube defects. ACOG Practice Bulletin No. 44. Obstetrics and Gynecology, 102(1): 203–210.
|Author||Sandy Jocoy, RN|
|Editor||Kathleen M. Ariss, MS|
|Associate Editor||Tracy Landauer|
|Primary Medical Reviewer||Sarah Marshall, MD - Family Medicine|
|Specialist Medical Reviewer||Siobhan M. Dolan, MD, MPH - Reproductive Genetics|
|Last Updated||May 14, 2008|
Last Updated: May 14, 2008