RIAKEY AFP IRMA Tube II
Immunoradiometric assay for quantitative determination of alpha-fetoprotein (AFP) in human serum or plasma
Alpha-Fetoprotein (AFP) is a glycoprotein of about 65.000 daltons molecular weight synthesized by the parenchymal cells of the fetal liver and the yolk sac. The properties and amino acid composition are similar to those of albumin. Synthesis of AFP occurs primarily in the liver and yolk sac of the fetus. The AFP level increases progressively as pregnancy progresses and reaches a peak at about the 14th week in the fetal serum and the 30th week in the maternal serum; it then progressively decreases. Elevated serum AFP levels subsequently reappear during pregnancy and in conjunction with several malignant diseases.
During pregnancy, AFP is synthesized mainly by fetal liver and the yolk sac and is secreted into fetal serum, where a peak (2~3 mg/mL) is reached in the 13th~14th week, thereafter gradually decreasing up to the time of birth. In the amniotic fluid, levels of AFP which finds its way there through urinary excretion of the fetus, follow the evolution of fetal serum with values about 200 times lower. AFP passes onto maternal serum mainly as a result of diffusion through the placenta. But AFP concentrations in pregnant women sera however follow a different course from that of fetal serum, being detectable to a greater extent than usual from the 10th~12th week and continuing to increase up to a maximum of 200~400ng/mL in the 30th~31th week and then falling off up to the time of delivery. If the fetus exhibits malformations of the neural tube (anencephaly, spina bifida), AFP diffusion into the amniotic fluid is found to increase, by causing a rise in maternal AFP. AFP levels in adults, normally below 15ng/mL, are found to be considerably higher in several tumoral forms (primary hematoma, testicular tumors) and non-tumoral pathologies (viral hepatitis, hepatic cirrhosis. telangiectasis, and ataxia). ** Pregnancy monitoring: For a prenatal diagnosis of anencephaly, it is advisable to test for AFP in maternal serum during the 16th~18th week; an AFP value higher than the normal limits for the period, if confirmed by a second assay, calls for a subsequent check by echography as well as AFP testing in amniotic fluid. It has to be borne in mind that other fetal pathologies, such as renal deficiencies, omphalocele, intrauterine death of the fetus or multiple pregnancies, may cause an increase in maternal AFP. During gestation, abnormally low serum AFP concentrations may indicate hydatidiform mole or Down's syndrome. ** Tumoral pathologies: Some 70~90% of patients with primary hepatoma exhibit high AFP levels, ranging up to a concentration of 1~5mg/mL. High AFP concentrations are also found in about 90% of patients suffering from germ cell testicular tumors. ** Non-tumoral pathologies: Non-tumoral hepatic affections such as viral hepatitis (acute or chronic) or cirrhosis, or even hereditary thyroxinemia, telangiectasis, ataxia and atresia of the biliary tracts, may produce an increase in serum AFP.
PRINCIPLE OF THE ASSAY
The RIAKEY AFP IRMA II is an non-competitive immunoradiometric (IRMA) method (“sandwich”). The method employs two highly specific monoclonal anti-AFP antibodies which recognize two different epitopes of the molecule. One antibody is coated on solid phase (coated tube), the other, specific for the AFP and labeled with Iodine-125, is used as a tracer. Antibody-coated polystyrene tubes serve as solid phase. The tracer antibody and the coated antibody react simultaneously with the AFP antigen present in the standards, control serum and samples. Unbounded material is removed by a washing step. The amount of bound tracer will be directly proportional to the AFP antigen concentration and the remaining radioactivity bound to the tubes is measured in a gamma scintillation counter.