α-fetoprotein
Summary
Alpha-fetoprotein (AFP) is a fetal serum glycoprotein analogous to adult albumin, produced by the fetal yolk sac and liver. Clinically it is a tumor marker for hepatocellular carcinoma and yolk sac (endodermal sinus) tumors, and a screening marker in maternal serum for neural tube defects (elevated) and Down syndrome (decreased).
Detail
AFP is the major fetal serum protein and physiologically falls to adult levels after birth. As a tumor marker, AFP is elevated in hepatocellular carcinoma (often >500 ng/mL), yolk sac tumors (Schiller-Duval bodies on histology), mixed germ cell tumors, and some hepatoblastomas; pure seminomas and pure dysgerminomas do NOT make AFP (so any AFP elevation rules out 'pure' seminoma). In pregnancy (maternal serum AFP, part of the quad screen): elevated MSAFP suggests open neural tube defects (anencephaly, open spina bifida), ventral wall defects (omphalocele, gastroschisis), or multiple gestation; decreased MSAFP is part of the Down syndrome quad (low AFP, low estriol, high beta-hCG, high inhibin A). Edward syndrome shows low AFP, low estriol, low hCG, normal inhibin A.
Sources
- First Aid for USMLE Step 1 2024
- Robbins Basic Pathology 10th ed
- UWorld Step 1
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