An alpha-fetoprotein (AFP) blood test is a test measures level of AFP in blood . AFP is used as a tumor marker to help detect and diagnose cancers of the liver, testes, and ovaries. The amount of AFP in the blood of a pregnant woman can help to detect problems as spina bifida and anencephaly in baby. 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 Edwards syndrome (trisomy 18).