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 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
Do I Need an Alpha-Fetoprotein Test?
An AFP test is a routine screening test that’s given to expectant
mothers between the 14th and 22nd weeks of their pregnancy. It appears to be
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
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
- 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
- biliary tract
Risks Are Associated with an Alpha-Fetoprotein Test?
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.
Is an Alpha-Fetoprotein Test Performed?
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 profession 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 usually available within one to two weeks.
Do the Test Results Mean?
For women who aren’t pregnant and men, the normal amount of AFP
is usually less than 40 micrograms per liter 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 Downs 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