What is an alpha-fetoprotein (AFP) test?

An alpha-fetoprotein (AFP) test is a blood test that measures the amount of AFP present in blood. It’s usually part of what’s called a triple screen or quad screen in the second trimester of pregnancy. However, it can also be useful for adults who aren’t pregnant.

The yolk sac, GI tract, and liver of an unborn baby produce AFP. It then circulates through the fetal and maternal blood. Individuals who aren’t pregnant still have some AFP in their blood, but levels are normally low. High levels of AFP in adults who aren’t pregnant usually indicate certain types of liver disease.

An AFP test is a routine screening test that’s given to expectant mothers between the 14th and 22nd weeks of their pregnancy. It is most accurate between the 16th and 18th weeks, so it’s important to know exactly when you became pregnant.

AFP testing is usually part of a quad screen. This screening exam also tests your levels of:

  • human chorionic gonadotropin (HCG)
  • estriol, which is a hormone produced by your placenta and your baby’s liver
  • inhibin A, which is a hormone produced by your placenta

Doctors will use your quad screen results, your age, and your ethnicity to help determine the chances that your unborn baby has a genetic birth defect. Defects detected by this type of screening can include neural tube defects, such as spina bifida, and chromosomal abnormalities, such as Down syndrome. The AFP results will help your doctor determine if you need further tests for these conditions. A positive test doesn’t necessarily mean your unborn baby will have a birth defect.

The AFP test is especially important for women who are at high risk of having children with birth defects, including women:

  • who are 35 or older
  • with a family history of birth defects
  • who used harmful medications or drugs during their pregnancies
  • who have diabetes

If you aren’t pregnant, an AFP test can help to diagnose and monitor certain liver conditions, such as liver cancer, cirrhosis, and hepatitis. It can also help detect several other cancers, including cancers of the:

  • testes
  • ovaries
  • biliary tract
  • stomach
  • pancreas

There are very few risks associated with having your blood drawn for an AFP test. You may feel slightly faint or have some soreness or pain at the puncture site. There’s a small chance of excessive bleeding or hematoma, which occurs when blood accumulates under your skin. There is also a very slight risk of infection at the puncture site.

You’ll need to get your blood drawn for an AFP test. Having blood drawn is an outpatient procedure that’s usually performed at a diagnostic lab. The procedure takes only a few minutes and is relatively painless. No special preparation is necessary before an AFP test.

A healthcare professional will use a small needle to withdraw blood from a vein, usually in your arm or hand. A laboratory specialist will analyze the sample. Results are typically available within one to two weeks.

For women who aren’t pregnant as well as men, the normal amount of AFP is usually less than 10 nanograms per milliliter of blood. If your AFP level is unusually high but you aren’t pregnant, it may indicate the presence of certain cancers or liver diseases.

If you’re pregnant you have higher-than-normal AFP levels, it can indicate a neural tube defect in your developing baby. However, the most common cause of elevated AFP levels is inaccurate dating of the pregnancy. AFP levels vary widely during pregnancy. The test will be inaccurate if you’ve been pregnant for a longer or shorter period of time than you thought.

If you’re pregnant and your AFP level is unusually low, it could indicate that your fetus has a chromosomal abnormality, such as Down syndrome or Edwards syndrome.

You can have an abnormal AFP reading due to a multiple pregnancy, such as having twins or triplets. An abnormal AFP reading can also be due to fetal death.

According to the American Pregnancy Association, results are abnormal for 25 to 50 pregnant women out of every 1,000 pregnant women given an AFP test. However, only between 1 in 16 and 1 in 33 women who have abnormal results will actually have a baby with a birth defect.

If you have abnormal test results, it doesn’t necessarily mean that your child will have a birth defect. It only indicates that more tests are necessary for your doctor to make a diagnosis. Your doctor may perform another AFP test followed by an ultrasound to record images of your unborn child.

Your doctor may order a more invasive test, such as an amniocentesis, if your results are still abnormal. In amniocentesis, your doctor uses a needle to withdraw a small amount of amniotic fluid from around the fetus for analysis.