Alpha-fetoprotein (AF-AFP) Testing Laboratory
Alpha-fetoprotein (AFP) is a protein produced by the fetal liver. The function of the protein is not known. It is found in high concentration in fetal blood and in lower concentration in fetal urine. AFP can be measured in amniotic fluid which is composed primarily of fetal urine. Amniotic fluid AFP (AF-AFP) may be elevated in open fetal body wall defects, most commonly open neural tube defects (NTD) and open ventral wall defects, due to transfer from exposed fetal vessels and tissue. AF-AFP is elevated in congenital nephrosis from increased glomerular filtration of this relatively small protein. In cases with elevated AF-AFP, the risk for an open NTD or other fetal abnormality depends on the degree of elevation in the AF-AFP MoM (multiple of the median), the results of amniotic fluid acetylcholinesterase testing, the detection of fetal hemoglobin and other significant risk factors.
Amniotic fluid, 2-5 ml, obtained from 14 – 24 weeks gestation. Results for specimens obtained prior to 14 weeks or after 24 weeks are less reliable.
Alpha-fetoprotein in amniotic fluid is measured in micrograms/ml (µg/ml) by a solid phase, two-site fluoroimmunometric assay. During the second trimester of a normal pregnancy, the AFP concentration in amniotic fluid decreases by about 10% with each successive gestational week. Conversion of the AFP concentration to multiples of the median (MoM) allows use of a single cut off level for all gestational weeks. AF-AFP values greater than or equal to 2.0 MoM are considered elevated and the pregnancy is considered at risk for an open fetal defect. Reflex testing for the presence of AChE and fetal hemoglobin is performed for all samples with elevated Alpha-fetoprotein (AF-AFP) lab testing results.
Transport amniotic fluid samples at ambient temperature by same day or overnight courier. In high temperatures, the specimen should be packed with a cold-pack and shipped at 2°-8°C.
Approximately 1-3 days
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