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 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 Edward syndrome (trisomy 18). An AFP test can 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 often 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), beta human chorionic gonadotropin (beta-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.

In some cases a combination of screening tests is done in the first trimester to look for Down syndrome. The integrated test uses an ultrasound measurement of the thickness of the skin at the back of the fetus's neck (nuchal translucency) and the levels of free beta-hCG and a protein called pregnancy-associated plasma protein A (PAPP-A). The sensitivity of this screening test is about the same as that of the second-trimester maternal serum quad screening.¹

Should I have the maternal serum screening test (triple or quad screen)?

Men, nonpregnant women, and children

In men, nonpregnant women, and children, alpha-fetoprotein 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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