AFP (Alpha-Fetoprotein) is a protein that is primarily produced by the liver and yolk sac of a developing fetus. It is commonly used as a biomarker in various clinical settings, particularly in the fields of oncology and obstetrics.

Clinical Significance of AFP:

1. Cancer Diagnosis and Monitoring:

• Hepatocellular Carcinoma (HCC): Elevated AFP levels are most commonly associated with primary liver cancer. Monitoring AFP is useful for screening high-risk patients (e.g., those with chronic hepatitis B or C or cirrhosis) and for assessing the effectiveness of treatment in known cases.
• Germ Cell Tumors: Increased AFP can also be seen in non-seminomatous germ cell tumors of the testis, ovary, or other locations.
• Other Malignancies: Although less common, AFP may be elevated in certain gastrointestinal cancers.

1. Prenatal Screening:

• Neural Tube Defects (NTDs): Elevated AFP levels in maternal blood or amniotic fluid can indicate neural tube defects such as spina bifida or anencephaly in the developing fetus.
• Other Fetal Conditions: Abnormally low AFP levels can be associated with conditions like Down syndrome or trisomy 18.
• Routine Screening: AFP is part of the triple or quad screen performed during the second trimester of pregnancy to evaluate the risk of certain fetal abnormalities.

How is the AFP Test Performed?

• Sample Type: Blood sample (serum) is typically used for testing AFP levels. In pregnant women, maternal serum or amniotic fluid can be tested.
• Test Procedure: The sample is analyzed in a laboratory using immunoassay techniques to quantify AFP levels.

Interpretation of AFP Results:

1. Elevated AFP Levels:

• Hepatocellular Carcinoma: Markedly elevated AFP (often >400 ng/mL) is suggestive of HCC.
• Germ Cell Tumors: Elevated levels are consistent with non-seminomatous types.
• Non-Cancerous Conditions: Can also be seen in liver diseases such as hepatitis or cirrhosis, though the elevations are usually moderate.

1. Low AFP Levels (in Pregnancy):

• May indicate an increased risk of chromosomal abnormalities like Down syndrome.
• Requires follow-up with ultrasound and/or amniocentesis for further evaluation.

Normal Reference Ranges:

• Adults (non-pregnant): Typically less than 10 ng/mL, but reference ranges may vary slightly by laboratory.
• Pregnant Women: Levels vary depending on the gestational age, and results are interpreted in context with other screening test markers.

Limitations of the AFP Test:

• Specificity: Elevated AFP alone is not diagnostic of cancer; other tests (e.g., imaging, biopsy) are required for confirmation.
• False Positives/Negatives: AFP levels can be influenced by factors such as multiple pregnancies or fetal age miscalculations.
• Other Tumor Markers: In some cases, additional markers such as beta-hCG or LDH may be tested alongside AFP for a comprehensive evaluation of germ cell tumors.

Summary:

AFP is a valuable marker for:

• Detecting and monitoring liver cancer and certain germ cell tumors.
• Prenatal screening for fetal abnormalities, with interpretation based on gestational age and combined with other test results.

In clinical practice, an elevated AFP level should prompt further investigation to determine the underlying cause and guide appropriate follow-up or treatment.