An alpha fetoprotein (AFP) test is a blood test used to measure the amount of AFP present in blood. It is usually done as part of a triple screen or quad screen in the second trimester of pregnancy. However, it can also be requested for adults who are not pregnant.
AFP is produced in the yolk sac and liver of an unborn baby. It then circulates through the fetal and maternal blood. Individuals who are not pregnant still have some AFP in their blood, but levels are normally low. High levels of AFP in adults who are not pregnant are associated with certain types of liver disease.
An AFP test is a routine screening test given to expectant mothers between the 14th and 22nd weeks of their pregnancy. It appears to be the most accurate between the 16th and 18th weeks, so it is important to know exactly when you became pregnant.
AFP testing is usually done as a component of a quad screen. Other tests performed during this screening exam include:
- human chorionic gonadotropin (HCG)
- inhibin A
Doctors will use your quad screen results, your age, and your ethnicity to help determine the chances that your unborn baby has a 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 further tests for these conditions are needed. A positive test does not necessarily mean your unborn baby will have a birth defect.
The AFP test is especially important for women who are at a high risk for 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
- with diabetes
If you are not pregnant, an AFP test can help to diagnose and monitor certain liver conditions, such as liver cancer, cirrhosis, and hepatitis. It can also be used to help detect certain cancers, including cancers of the:
- biliary tract
You will need to get your blood drawn for an AFP test. Having blood drawn is an outpatient procedure, 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 nurse will use a small needle to withdraw blood from a vein (usually in your arm or hand), and a laboratory specialist will analyze the sample. Results are usually available within one to two weeks.
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 site where your blood was drawn. There is a small chance of excessive bleeding or hematoma (blood that accumulates under the skin). There is also a very slight risk of infection at the puncture site.
For men and nonpregnant women, the normal amount of AFP is usually less than 40 micrograms per liter of blood. If your AFP level is unusually high but you are not pregnant, it may indicate the presence of certain cancers or liver conditions.
Higher-than-normal AFP levels in pregnant women can indicate a neural tube defect in the 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 have been pregnant for a longer or shorter period of time than you thought.
If you are pregnant and your AFP level is unusually low, it could indicate that your fetus has a chromosomal abnormality, such as Down or Edwards syndrome. Abnormal AFP readings can also be due to a multiple pregnancy (having twins, triplets, etc.) or fetal death.
According to the American Pregnancy Association, out of every 1,000 pregnant women given an AFP test, the results are abnormal in 25 to 50 cases. Of these abnormal cases, however, only between one in 16 and one in 33 women will actually have a baby with a birth defect (APA).
If your test results are abnormal, it does not 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. If the results are still abnormal, your doctor may order a more invasive test, such as amniocentesis.
Amniocentesis uses a needle to withdraw a small amount of amniotic fluid from around the fetus for analysis.