Tumor Marker – Part 12 – Alpha-Fetoprotein (AFP)

Alpha-Fetoprotein

1. This is a glycoprotein. This consists of the single polypeptide chain and has a 4% carbohydrate.
   1. This is produced by the yolk sac and liver in the fetus.
   2. It is normal after about 18 months of birth.

2. It is close to albumin, genetically, and structurally.
   1. 1. Gene coding for both is chromosome 4q.
      2. Its concentration is 10% that of the albumin.
3. The function of the AFP:
   1. Its main role is to bind and transport substances that are not water-soluble, like steroids hormones, lipids, vitamins, and bilirubin.
   2. Maternal serum AFP is lower than expected in the Down’s syndrome.
   3. Maternal serum AFP is raised or higher level in the neural tube defect.
4. Level > 1000 µg/L indicate malignancy.
   1. At this level, 50% of the liver cell carcinomas are diagnosed.
   2. It is ideal to diagnose the liver tumor below the size of 5 cms.
   3. To find these small tumors cut-off value has to be set at a lower level between 200 to 1000 µg/L.
5. In healthy individuals is 10 µg/L.
6. This is a tumor marker for:
   1. Liver cell carcinoma. >500 ng/mL is diagnostic of liver cell carcinoma.
   2. Germ cell tumor (nonseminomatous tumor).
   3. Choriocarcinoma element in seminoma, yolk sac, teratoma, and embryonal cell carcinoma.
7. AFP is useful for liver cell carcinoma:
   1. Diagnosing.
   2. Prognosis.
   3. Monitor therapy.
8. Normal
   1. Adult = <40 ng/mL  (<40 µg/L)
   2. Child <1 year = <30 ng/mL