AFP

Alpha-Fetoprotein (AFP)

Other

What is Alpha-Fetoprotein (AFP)?

Alpha-fetoprotein (AFP) is a glycoprotein produced in large quantities by the fetal liver and yolk sac during embryonic development. It is the dominant serum protein in the developing fetus, serving as a carrier molecule for bilirubin, fatty acids, steroids, and heavy metals—analogous to albumin in adults. AFP levels are extremely high in fetal blood, peak around 12–14 weeks of gestation, and decline progressively after birth, reaching normal adult levels (typically <10 ng/mL) by 12–18 months of age.

In adult clinical medicine, AFP is used primarily as a tumor marker and screening tool. It is elevated in hepatocellular carcinoma (HCC), the most common primary liver cancer, and in certain germ cell tumors including yolk sac tumors and mixed germ cell tumors. AFP is a cornerstone of HCC surveillance programs, measured every six months alongside liver ultrasound in high-risk populations such as patients with cirrhosis or chronic hepatitis B. In obstetrics, maternal serum AFP is part of prenatal screening panels—elevated levels may indicate neural tube defects, while low levels may suggest chromosomal abnormalities.

Why It Matters

AFP is one of the most clinically important tumor markers. Hepatocellular carcinoma is the sixth most common cancer and the third leading cause of cancer death worldwide, and early detection through AFP surveillance in cirrhotic patients can identify tumors at treatable stages, significantly improving survival. AFP above 400 ng/mL in a cirrhotic patient with a liver mass is essentially diagnostic for HCC. In testicular germ cell tumors, AFP is used for diagnosis, staging, and monitoring treatment response—rising AFP after chemotherapy indicates treatment failure or relapse.

Normal Reference Ranges

GroupRangeUnit
Adults (non-pregnant)<10ng/mL
Pregnant Women (15–20 weeks)10–150ng/mL
NeonatesUp to 100,000ng/mL

Reference ranges may vary by laboratory. Always compare results to the ranges provided by your testing facility.

What High AFP Levels Mean

Common Causes

  • Hepatocellular carcinoma (HCC)
  • Germ cell tumors (yolk sac tumor, mixed germ cell tumor)
  • Hepatoblastoma (childhood liver cancer)
  • Chronic hepatitis (mild elevation)
  • Cirrhosis (mild to moderate elevation)
  • Pregnancy (physiologic elevation)
  • Neural tube defects in fetus (elevated maternal AFP)
  • Acute hepatic necrosis with liver regeneration

Possible Symptoms

  • Right upper quadrant abdominal pain or fullness (HCC)
  • Unexplained weight loss and decreased appetite
  • Jaundice and ascites (advanced liver disease)
  • Testicular mass or swelling (germ cell tumor)
  • Abdominal mass in a child (hepatoblastoma)
  • Often asymptomatic in early-stage disease (detected by screening)

What to do: AFP >400 ng/mL in a cirrhotic patient with a characteristic liver mass on imaging is diagnostic for HCC per AASLD guidelines. AFP between 20–400 ng/mL requires further evaluation with contrast-enhanced CT or MRI. Rising AFP in a young male should prompt testicular ultrasound and evaluation for germ cell tumor with β-hCG and LDH. Mildly elevated AFP (10–20 ng/mL) in chronic liver disease may reflect hepatic inflammation rather than malignancy—trend over time. In prenatal screening, abnormal maternal AFP warrants ultrasound and possibly amniocentesis.

What Low AFP Levels Mean

Common Causes

  • Normal finding in healthy non-pregnant adults
  • Low maternal AFP may suggest fetal chromosomal abnormality (Down syndrome, trisomy 18)

Possible Symptoms

  • No symptoms from low AFP in adults

What to do: Low AFP in non-pregnant adults is normal and requires no action. In prenatal screening, low maternal AFP as part of a quad screen may indicate increased risk for Down syndrome or trisomy 18—further evaluation with cell-free fetal DNA testing or amniocentesis is offered based on overall screening risk assessment.

When Is AFP Testing Recommended?

  • Every 6 months for HCC surveillance in patients with cirrhosis
  • When a liver mass is found in a patient with chronic liver disease
  • When evaluating testicular or mediastinal germ cell tumors
  • As part of maternal serum screening during pregnancy (15–20 weeks)
  • When monitoring treatment response in AFP-producing tumors
  • When hepatoblastoma is suspected in a child

Frequently Asked Questions

The AASLD recommends HCC surveillance using abdominal ultrasound with or without AFP every 6 months in high-risk populations, including patients with cirrhosis from any cause and chronic hepatitis B carriers. Ultrasound alone detects early HCC with about 58% sensitivity, while adding AFP improves sensitivity to approximately 63–70%. However, about 30–40% of HCCs are AFP-negative, so AFP alone is insufficient for screening. A rising AFP trend should trigger cross-sectional imaging even if ultrasound appears normal.
Elevated maternal serum AFP during pregnancy (measured at 15–20 weeks) may indicate several conditions: open neural tube defects (spina bifida, anencephaly) where AFP leaks from exposed fetal tissue, abdominal wall defects (omphalocele, gastroschisis), multiple gestations, or incorrect dating. Abnormal results prompt ultrasound evaluation and possibly amniocentesis for definitive diagnosis. Low maternal AFP, conversely, may indicate increased risk for chromosomal abnormalities such as Down syndrome.
Yes, AFP can be mildly to moderately elevated (typically 10–200 ng/mL) in non-cancerous liver conditions including chronic hepatitis B and C, alcoholic hepatitis, cirrhosis from any cause, and acute liver injury with regeneration. This occurs because regenerating hepatocytes can revert to producing fetal proteins like AFP. This is why AFP alone cannot diagnose HCC—the trend over time and the magnitude of elevation are important. AFP levels >400 ng/mL in the setting of cirrhosis and a liver mass are highly specific for HCC.
AFP-L3 is a specific glycoform of AFP that is preferentially produced by hepatocellular carcinoma cells due to their altered glycosylation pathways, while benign liver conditions tend to produce AFP-L1. An AFP-L3 fraction >10% of total AFP has approximately 95% specificity for HCC, making it more specific than total AFP alone. AFP-L3 is particularly useful when total AFP is in the equivocal range (20–200 ng/mL), helping distinguish malignant from benign causes of AFP elevation. It is FDA-approved as a risk assessment tool for HCC in chronic liver disease.
AFP is produced by yolk sac tumor cells and is elevated in pure yolk sac tumors, mixed germ cell tumors with a yolk sac component, and embryonal carcinomas. It is NOT elevated in pure seminomas or pure choriocarcinomas—AFP elevation in a patient with a seminoma suggests a mixed tumor. AFP, along with β-hCG and LDH, forms the tumor marker triad used for germ cell tumor staging (the International Germ Cell Consensus Classification). Post-treatment, AFP should normalize (half-life approximately 5–7 days). Failure to normalize or subsequent rise indicates residual disease or relapse and changes management.

Related Biomarkers

ALTAlanine AminotransferaseASTAspartate AminotransferaseTBILBilirubinALBAlbuminAFPAlpha-Fetoprotein

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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Reference ranges may vary between laboratories. Always consult your healthcare provider for interpretation of your specific test results.

Disclaimer: SymptomGPT is not a medical diagnosis tool and does not provide medical advice. Always consult a qualified healthcare professional. If you are experiencing a medical emergency, call 911 immediately.