AFP

Alpha-Fetoprotein

Immune & Inflammation

What is Alpha-Fetoprotein?

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 fetus, analogous to albumin in adults, serving as a carrier for various molecules including bilirubin, fatty acids, steroids, and heavy metals. AFP levels are extremely high in fetal blood, peak around 12–14 weeks of gestation, and decline after birth, reaching normal adult levels (typically <10 ng/mL) by 12–18 months of age.

In adult clinical medicine, AFP serves two primary roles: as a tumor marker and as a surveillance tool. As a tumor marker, AFP is elevated in hepatocellular carcinoma (HCC), the most common primary liver cancer, and in certain germ cell tumors (yolk sac tumors, mixed germ cell tumors). AFP is a key component of HCC surveillance programs in high-risk populations (cirrhosis patients, chronic hepatitis B carriers), where it is measured every six months alongside liver ultrasound. In obstetrics, maternal serum AFP is part of prenatal screening—elevated levels may indicate neural tube defects (spina bifida, anencephaly), while low levels may suggest chromosomal abnormalities (Down syndrome, trisomy 18).

Why It Matters

AFP is one of the most important tumor markers in clinical medicine. Hepatocellular carcinoma is the sixth most common cancer and the third leading cause of cancer death worldwide. Early detection through AFP surveillance in cirrhotic patients can identify HCC at a treatable stage, significantly improving survival. AFP above 400 ng/mL in a cirrhotic patient with a liver mass is essentially diagnostic for HCC without requiring biopsy. In 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<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 (in children)
  • Chronic hepatitis (mild elevation)
  • Cirrhosis (mild to moderate elevation)
  • Pregnancy (physiologic elevation)
  • Neural tube defects in fetus (elevated maternal AFP)
  • Acute hepatic necrosis (regenerating liver)

Possible Symptoms

  • Right upper quadrant pain or fullness (in HCC)
  • Unexplained weight loss
  • Jaundice and ascites (in advanced HCC)
  • Testicular mass (in 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 using the LI-RADS classification. Rising AFP in a young male should prompt testicular ultrasound and evaluation for germ cell tumor (check β-hCG and LDH as well). In surveillance, AFP is measured every 6 months in patients with cirrhosis or chronic hepatitis B. Mildly elevated AFP (10–20 ng/mL) in chronic liver disease may reflect hepatic inflammation and regeneration rather than cancer—trend over time.

What Low AFP Levels Mean

Common Causes

  • Normal finding in healthy adults
  • Low maternal AFP may suggest fetal chromosomal abnormality (Down syndrome)

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 (trisomy 21) or trisomy 18—further evaluation with cell-free fetal DNA testing or amniocentesis is offered based on overall screening risk.

When Is AFP Testing Recommended?

  • Every 6 months for HCC surveillance in cirrhotic patients
  • When a liver mass is found in a patient with liver disease
  • When evaluating testicular or mediastinal germ cell tumors
  • As part of maternal serum screening during pregnancy
  • When monitoring treatment response in AFP-producing tumors

Frequently Asked Questions

The American Association for the Study of Liver Diseases (AASLD) recommends surveillance for hepatocellular carcinoma in high-risk populations using abdominal ultrasound with or without AFP every 6 months. High-risk groups include patients with cirrhosis from any cause, chronic hepatitis B carriers (even without cirrhosis in certain populations), and patients with non-alcoholic steatohepatitis (NASH) with advanced fibrosis. Ultrasound alone has a sensitivity of about 58% for early HCC, while adding AFP improves sensitivity to approximately 63–70%. AFP alone has limited sensitivity (around 60%) because not all HCCs produce AFP—approximately 30–40% of HCCs are AFP-negative, particularly small tumors and the fibrolamellar variant. Despite this limitation, a rising AFP trend is a red flag that should trigger cross-sectional imaging even if ultrasound is unremarkable.
AFP is the major serum protein of the developing fetus, produced by the fetal liver and yolk sac. During pregnancy, some fetal AFP crosses the placenta into the maternal bloodstream, causing measurable elevation in maternal serum. Maternal AFP levels rise throughout pregnancy, typically peaking at 28–32 weeks. In prenatal screening (performed at 15–20 weeks), maternal AFP is one component of the "quad screen" (along with β-hCG, unconjugated estriol, and inhibin A). Abnormally high maternal AFP may indicate neural tube defects (open spina bifida or anencephaly, where AFP leaks from exposed fetal neural tissue), abdominal wall defects (omphalocele, gastroschisis), multiple gestations, or incorrect dating. Abnormally low AFP may suggest chromosomal abnormalities.
AFP-L3 is a specific glycoform (isoform) of AFP that is bound by the lectin Lens culinaris agglutinin. While benign liver conditions (hepatitis, cirrhosis, regenerating nodules) tend to produce AFP-L1 (the main fraction), hepatocellular carcinoma cells preferentially produce AFP-L3 due to altered glycosylation pathways. An AFP-L3 fraction >10% of total AFP has approximately 95% specificity for HCC, making it more specific than total AFP alone. The AFP-L3 percentage can help distinguish HCC from benign causes of AFP elevation, particularly when total AFP is in the equivocal range (20–200 ng/mL). It is FDA-approved as a risk assessment tool for HCC development in chronic liver disease patients. Some surveillance protocols incorporate AFP-L3 alongside total AFP and ultrasound.

Related Biomarkers

ALTAlanine AminotransferaseASTAspartate AminotransferaseTBILBilirubinALBAlbumin

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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.