Alpha-fetoprotein (AFP) is an important plasma protein synthesised by the yolk sac and fetal liver. In adults, its main utility is as a tumour marker, primarily for hepatocellular carcinoma or teratoma. Functionally it is the fetal homologue of albumin, i.e. it acts as a major carrier protein in the antenatal circulation. It is encoded by the AFP gene 1.
Interpretation
Elevation
This may occur in a broad spectrum of conditions:
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liver tumours (hepatocellular carcinoma, hepatoblastoma)
<10 ng/mL is within normal limits
>20 ng/mL is above normal limits but has low specificity for tumour since it may occur in a setting of diffuse liver injury
increasing AFP over time, especially with stable AST and ALT is suspicious
AFP has a low sensitivity and specificity for hepatic malignancy
in the presence of hepatocellular carcinoma, an elevated AFP level is indicative of an aggressive tumour 5
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pancreatic tumours
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antenatal conditions (maternal serum AFP (MSAFP))
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normal pregnancy
rises from 12 weeks and peaks during the early 3rd trimester
increased in multifetal pregnancy
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ovarian Sertoli-Leydig cell tumour (rarely) 4
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other tumours
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non-malignant conditions
Reduction
This may be seen in pregnancy.
AFP reduction may be associated with:
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certain chromosomal anomalies
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