Description
Alpha-Fetoprotein (AFP) is a glycoprotein with a molecular weight of 70 kDA. AFP shares considerable sequential homology with albumin and is normally produced during fetal development by the hepatocytes, yolk sac and to a lesser extent by the gastrointestinal tract. AFP appears as a major serum protein in the fetus, but its concentration declines rapidly towards birth. Serum concentrations reach a peak level of up to 10 mg/ml at twelve weeks of gestation.
This peak level gradually decreases to less than 25 ng/ml after one year of postpartum. Thereafter, the levels reduce further to less than 10 ng/ml.
Ever since its first reported association with tumors, by Tatarinov in 1964 based on his work with liver carcinomas, AFP has been a subject of discussion with relation to many different tumors. Abnormal AFP levels have been associated with hepatocellular carcinoma, ovarian cancer, gastrointestinal cancer and pulmonary cancer and, most recently, with non-seminomatous testicular cancer. Elevated levels of AFP are found in patients with primary heptatoma and yolk sac-derived germ tumors. AFP is the most useful marker for the diagnosis and management of hepatocellular carcinoma.
AFP is also elevated in pregnant women. Presence of abnormally high AFP concentrations in pregnant women provides a risk marker for Down syndrome.
In this method, AFP calibrator, patient specimen or control is first added to a streptavidin coated well. Biotinylated monoclonal and enzyme labeled antibodies (directed against distinct and different epitopes of AFP) are added and the reactants mixed. Reaction between the various AFP antibodies and native AFP forms a sandwich complex that binds with the streptavidin coated to the well. After the completion of the required incubation period, the enzyme-AFP antibody bound conjugate is separated from the unbound enzyme-AFP conjugate by aspiration or decantation. The activity of the enzyme present on the surface of the well is quantitated by reaction with a suitable substrate to produce light measurable with a luminometer.
The employment of several serum references of known alpha-fetoprotein (AFP) levels permits the construction of a dose response curve of activity and concentration. From comparison to the dose response curve, an unknown specimen's activity can be correlated with AFP concentration