Genemed Biotechnologies

Second Trimester Prenatal Screening Kit for Down's Syndrome

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PNS-2 COMBO EIA is an in vitro immunoassay kit for quantitative determination of AFP and free beta-hCG concentrations in human serum. This kit is based on a solid phase, enzyme-linked immunosorbent assay (ELISA).

Background
In neonate plasma, alpha-fetoprotein (AFP), a single-chain glycoprotein with a carbohydrate content of 4-5% and a molecular weight of 68 kDa, is an oncofetal protein found in high concentration in patients with certain neoplastic and non-neoplastic disorders. Under normal circumstances, only trace amounts are observed in normal human serum. Detection and measurement of serum AFP levels have been found to be useful in the diagnosis, prognosis, and follow-up of patients with hepatoma and germ cell tumors. Elevation of serum AFP levels was found to be approximately 10-20% for patients with nonmalignant liver diseases, while it was about 50-90% among patients with hepatoma. Serum AFP usually increases as the tumor progresses in hepatoma patents. Complete surgical resection of the tumors produces an immediate decrease in AFP levels. Recurrence of elevated AFP levels almost certainly means tumor recurrence. AFP levels measured in maternal blood and in amniotic fluid has been useful in detection of a number of fetal disorders. Many studies have confirmed the utility of AFP in the early detection of open neural tube defects (NTD). Thus, AFP testing during pregnancy is recommended as an effective way to identify women who are potentially at risk of carrying a fetus affected with a NTD.

Human Chorionic Gonadotropin (hCG) is a glycoprotein hormone normally produced by 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 of 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 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.