Definition of AFP (alpha-fetoprotein)

AFP (alpha-fetoprotein): AFP is a plasma protein
that is
normally produced by the fetus. It serves as the basis for some
valuable tests.
AFP is manufactured principally in the
fetus's liver and, also, in the fetal gastrointestinal (GI) tract and
the yolk sac, a structure temporarily present during embryonic
development.
The level of AFP is typically high in the fetus's blood. It goes
down in
the baby's blood after birth. And by a year of age, it is virtually
undetectable.
During pregnancy, AFP crosses the placenta from the fetal
circulation and appears in the mother's blood. The level of AFP in
the mother's blood (the maternal serum AFP) provides a screening test
for a number of disorders including:
Open neural tube defects (anencephaly and spina
bifida); and
Down syndrome (and other chromosome abnormalities).
The maternal serum AFP (MSAFP) tends to be:
High with open neural tube
defects such as anencephaly and spina bifida (meningomyelocele); and
Low with Down syndrome (trisomy 21, an extra chromosome number
21).
AFP production is essentially nil after a year of age. However,
it starts up again under the stimulus of some diseases in the
liver. It
may, for example, be produced by the liver in viral hepatitis and
cirrhosis of
the liver. AFP is also made by primary liver tumors
(hepatomas) and by germ
cell tumors (teratocarcinoma and embryonal cell carcinomas). A
person's
serum AFP level can therefore be used to help detect these conditions
and monitor their
treatment.