Special remarks:

1.     Description

The ¹²⁵I‑AFP IRMA system provides direct quantitative in vitro determination of human alpha-fetoprotein (AFP) in human serum. AFP can be assayed in the range of 0‑500 IU/ml using 50 µl serum samples.

2.     Introduction

Alpha-fetoprotein (AFP) is a glycoprotein with a molecular mass of 65000. It is normally produced in large amounts by the fetal liver. AFP level increases progressively and reaches a peak at the 30^th week in the maternal serum, thereafter, it decreases gradually. An elevated maternal serum AFP is associated with neural tube defect (spina bifida) and placental abnormalities, whereas the decreased AFP levels in both maternal serum and amniotic fluid are related to fetal chromosomal abnormalities.

Patients affected by liver carcinoma, testicular or ovarian teratocarcinoma commonly present high AFP levels. Although less frequently, an increased AFP concentration may also be observed in hepatitis, gastric, breast and bronchial tumors.

This kit can  be used in the risk assessment  of Down’s Syndrome (Trisomy 21) in combination with other biochemical and ultrasound parameters as specified above, taking also into account other data like maternal age and weight and using a validated software for Down’s Syndrome risk assessment:

1.     Triple test: maternal serum AFP, hCG and unconjugated Estriol determination in the second trimester of pregnancy.

2.     Quadruple test: maternal serum AFP, hCG, unconjugated Estriol and Inhibin-A determination in the second trimester of pregnancy.

3.     Integrated test: maternal serum PAPP-A determination and nuchal translucency (NT) thickness measurement by an ultrasound scan in the first trimester of pregnancy and maternal serum AFP, hCG, unconjugated Estriol and Inhibin-A determination in the second trimester.

3.    Principle of method

The technology uses two high affinity monoclonal antibodies in an immunoradiometric assay (IRMA) system.

The ¹²⁵I labeled signal-antibody binds to an epitope of the AFP molecule spatially different from that recognized by the biotin-capture-antibody. The two antibodies react simultaneously with the antigen present in standards or samples, which leads to the formation of a capture antibody - antigen - signal antibody complex, also referred to as a “sandwich”.

During a 2-hour incubation period with shaking immuno-complex is immobilized to the reactive surface of streptavidin coated test tubes. Reaction mixture is then discarded, test tubes washed exhaustively, and the radioactivity is measured in a gamma counter.

The concentration of antigen is directly proportional to the radioactivity measured in test tubes. By constructing a calibration curve plotting binding values against a series of calibrators containing known amount of AFP, the unknown concentration of AFP in patient samples can determined.