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Alpha fetoprotein

Definition

Alpha fetoprotein (AFP) is a protein normally produced by the liver and yolk sac of a developing baby during pregnancy. AFP levels decrease soon after birth. AFP probably has no normal function in adults.

A test can be done to measure the amount of AFP in your blood.

See also: Quadruple screen

Alternative Names

Fetal alpha globulin; AFP

How the test is performed

A blood sample is needed. For information on how this is done, see: Venipuncture

How to prepare for the test

There is no special preparation.

How the test will feel

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed

Your doctor may order this test to:

  • Screen for problems in the baby during pregnancy
  • Diagnose certain liver disorders
  • Screen for and monitor some cancers

During pregnancy, this AFP test can be done along with amniocentesis to help detect spina bifida or other birth defects in the developing baby.

Normal Values

The normal values in males or nonpregnant females is generally less than 40 micrograms/liter.

The examples above are common measurements for results of these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.

What abnormal results mean

Greater than normal levels of AFP may be due to:

During pregnancy, abnormal levels of AFP (as part of a quadruple screen) may be due to:

  • Birth defects, including:
  • Genetic disorders, including Down syndrome
  • Inaccurate due date
  • Intrauterine death (usually results in a miscarriage )
  • Multiple pregnancy (twins, triplets, etc.)

What the risks are

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but may include:

  • Excessive bleeding
  • Fainting or feeling lightheaded
  • Hematoma (blood accumulating under the skin)
  • Infection (a slight risk any time the skin is broken)

References

Simpson JL, Otaño L. Prenatal genetic diagnosis. In: Gabbe SG, Niebyl JR, Simpson JL, eds. . 5th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2007:chap 7.

Lee P, Pincus MR, McPherson RA. Diagnosis and management of cancer using serologic tumor markers. In: McPherson RA, Pincus MR, eds. . 21st ed. Philadelphia, Pa: Saunders Elsevier; 2006:chap 74.

Cunningham FG, Leveno KJ, Bloom SL, et al. Prenatal diagnosis and fetal therapy. In: Cunningham FG, Leveno KL, Bloom SL, et al, eds. . 23rd ed. New York, NY: McGraw-Hill; 2010:chap 13.

Encyclopedia content is provided as information only and not intended to replace the advice and instruction from your personal physician.