alpha-fetoprotein (AFP, a1-Fetoprotein)
المؤلف:
Kathleen Deska Pagana, Timothy J. Pagana, Theresa Noel Pagana.
المصدر:
Mosbys diagnostic and laboratory test reference
الجزء والصفحة:
15th edition , p37-38
2025-10-22
58
Type of test Blood
Normal findings
Adult: < 40 ng/mL or < 40 mcg/L (SI units)
Child (< 1 year): < 30 ng/mL
(Ranges are stratified by weeks of gestation and vary according to laboratory.)
Test explanation and related physiology
Alpha-fetoprotein (AFP) is an oncofetal protein normally produced by the fetal liver and yolk sac. It is the dominant fetal serum protein in the first trimester of life and diminishes to very low levels by the age of 1 year. It is also normally found in very low levels in the adult.
AFP is an effective screening serum marker for fetal body wall defects. The most notable of these are neural tube defects, which can vary from a small myelomeningocele to anencephaly. If a fetus has an open body wall defect, fetal serum AFP leaks out into the amniotic fluid and is picked up by the maternal serum. AFP from fetal sources can normally be detected in the amniotic fluid or the mother’s blood after 10 weeks’ gestation. Peak levels occur between 16 and 18 weeks’ gestation. Maternal serum reflects the changes in amniotic AFP levels. When elevated maternal serum AFP levels are identified, further evaluation with repeat serum AFP levels, amniotic fluid AFP levels, and ultra sound is warranted.
Elevated serum AFP levels in pregnancy may also indicate multiple pregnancy, fetal distress, fetal congenital abnormalities, or intrauterine death. Low AFP levels after correction for age of gestation, maternal weight, race, and presence of diabetes are found in mothers carrying fetuses with trisomy 21 (Down syn drome). See maternal screen testing and nuchal translucency for other pregnancy screening tests. AFP is also used as a tumor marker.
Interfering factors
• Fetal blood contamination, which may occur during amniocentesis, can cause increased AFP levels.
• Recent administration of radioisotopes can affect values. Procedure and patient care
• See inside front cover for Routine Blood Testing.
• Fasting: no
• Blood tube commonly used: red
• If AFP is to be performed on amniotic fluid, follow the procedure and patient care for amniocentesis.
• Include the gestational age on the laboratory slip.
Abnormal findings
Increased maternal AFP levels
- Neural tube defects (e.g., anencephaly, encephalocele, spina bifida, myelomeningocele)
- Abdominal wall defects (e.g., gastroschisis or omphalocele)
- Multiple pregnancy
- Threatened abortion
- Fetal distress or congenital anomalies
- Fetal death
Decreased maternal serum AFP levels
- Trisomy 21 (Down syndrome)
- Fetal wastage
Increased nonmaternal AFP levels
- Primary hepatocellular cancer (hepatoma)
- Germ cell or yolk sac cancer of the ovary
- Embryonal cell or germ cell tumor of the testes
- Other cancers (e.g., stomach, colon, lung, breast, or lymphoma)
- Liver cell necrosis (e.g., cirrhosis or hepatitis)
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