Genemed Biotechnologies

First Trimester Prenatal Screening Kit for Down's Syndrome

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High Specificity

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PNS-1 COMBO EIA is an in vitro immunoassay kit for quantitative determination of PAPP-A and free beta-hCG concentrations in human serum. This kit is based on a solid phase, enzyme-linked immunosorbent assay (ELISA).

Background
Pregnancy-associated plasma protein-A (PAPP-A) is a large glycoprotein produced mainly by the trophoblast during pregnancy and is released into the maternal circulation. The circulating PAPP-A is a disulfide-bonded complex consisting of two PAPP-A subunits and two subunits of a glycosylated proform of eosinophil major basic protein (proMBP). In serum, the concentration of PAPP-A/proMBP rises throughout pregnancy. PAPP-A has been shown to be a potent marker during the first trimester of pregnancy for Down's Syndrome and other abnormalities. Studies have shown that serum PAPP-A levels are depressed in women with fetal Down's Syndrome in the first trimester. The diagnostic rate for Down's Syndrome is significantly higher for PAPP-A than for beta-hCG and alpha-fetoprotein (AFP), individually, in the first trimester. However, the detection rate for Down's Syndrome is even higher when screening for PAPP-A is combined with other proteins in the first trimester of pregnancy. Human Chorionic Gonadotropin (hCG) is a glycoprotein hormone normally produced by the placenta during pregnancy. The hormone is present in blood and urine around 7 to 13 days following implantation of the fertilized ovum. Structurally intact hCG molecules consist of two noncovalently linked polypeptides, the alpha- and beta-chain subunits. Measurement of intact hCG and the alpha subunit of hCG appears to give similar results in blood and urine, but this is not the case for the beta subunit. hCG and its free subunits do not appear to be useful as serological markers for nontrophoblastic tumors; however, the absolute increase of beta-hCG level in Choriocarcinoma patients clearly differentiates it from normal pregnancy.

Assay Principle
First, a sample is incubated in each well to allow capture of the analyte by the capture antibody, which is precoated and bound to each well. Subsequently, a secondary antibody, conjugated to the horseradish peroxidase (HRP), is added to form a sandwich complex. The unbound conjugate is then washed off with washing buffer. Upon addition of substrate/chromogen, a blue color develops. The color development is stopped with the addition of 2N HCl (Stopping Solution), which changes the color to yellow. The concentration of the analyte present in the sample is proportional to the intensity of the yellow color. Absorbance is measured at 450 nm.