AlphaFetoprotein

Alpha-fetoprotein (AFP) is a glycoprotein produced primarily by the fetal liver and yolk sac during fetal development. In adults, AFP levels are normally low. AFP circulates in the fetal and maternal circulation and crosses the placenta, allowing maternal serum AFP measurements to reflect fetal physiology.

In pregnancy, AFP is routinely measured as part of prenatal screening. Maternal serum AFP (MSAFP) levels rise with gestational age and are interpreted together with other markers and ultrasound findings. Elevated MSAFP can indicate open neural tube defects (such as spina bifida or anencephaly) or ventral wall defects, but can also result from multiple gestation or dating errors. Low AFP levels may be associated with certain fetal chromosomal abnormalities, such as trisomy 21. Abnormal results typically lead to further investigations, including detailed ultrasound and sometimes amniocentesis to assess amniotic fluid AFP and other indicators.

In adults, elevated AFP is most commonly associated with malignancy, particularly hepatocellular carcinoma and certain germ cell tumors (for example, nonseminomatous testicular cancer and yolk sac tumors). AFP is used as a tumor marker to aid diagnosis, guide treatment, and monitor for recurrence. AFP-L3, a specific AFP isoform, and related markers (such as PIVKA-II/DCP) can provide additional information, particularly in hepatocellular carcinoma, though none are perfectly specific.

Limitations include lack of specificity, gestational and assay-related variations, and false positives in pregnancy or liver disease. AFP levels are interpreted in context with imaging studies and clinical findings.