Alpha-fetoprotein (AFP)

AFP is a single chain glycoprotein of 591 amino acids that is structurally related to albumin. Synthesis of AFP occurs primarily in the liver and yolk sac of the fetus. It is secreted into fetal serum, reaching a peak at about 13 weeks gestation and gradually declining thereafter. After birth, circulating concentrations decrease with a half-life of 5 days to adult levels by 8-10 months of age. The higher values in early childhood must be considered when using AFP measurement in testicular yolk sac tumour, the commonest testicular neoplasm in infants. Elevated circulating levels of AFP are observed in several malignant diseases, most commonly in hepatocellular carcinoma (HCC) and germ cell tumours where measurement is an important part of management. AFP is also used in the diagnosis of hepatoblastoma. Elevated serum AFP occurs in pregnancy and transient increases in serum AFP may occur in liver regeneration, hepatitis, chronic liver disease and cirrhosis (especially in hepatitis), biliary tract obstruction, alcoholic liver disease, ataxia telangiectasia and hereditary tyrosinaemia.

Testicular and other germ cell tumours (GCT)

Diagnosis: serum AFP (and hCG) marker measurement are an essential part of the clinical workup of GCT.
Prognosis and staging: elevated levels (with hCG) are prognostic and are used for risk stratification.
Treatment monitoring: the rate of AFP (or hCG) decline reflects response to therapy. If raised, markers should be monitored weekly until within the reference interval.
Surveillance: serial monitoring with AFP (and hCG) at decreasing frequency for a minimum of 10 years is used in both marker positive and negative disease.

HCC

Diagnosis: measurement of AFP and abdominal ultrasound is used in patients at high risk of HCC, eg. liver cirrhosis related to hepatitis B/C. A rising AFP should be investigated even if initial imaging is negative.
Prognosis and staging: AFP concentration is an independent predictor of poor prognosis.
Treatment monitoring: after successful resection, AFP concentrations decrease with a half-life of 3-4 days.
Surveillance: measurement of AFP at follow-up visits is recommended to monitor disease status.

Adult serum (non-pregnant): <14 µg/L

Non-infant CSF (>2 months of age): <3 µg/L

CSF analysis: Samples should be as fresh as possible. Avoid repeated freeze/thaw cycles.

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