Alpha-fetoprotein (AFP) values are compared to the median value of the unaffected population at a given gestational age and the multiple of the median (MoM) is obtained and classified as either screen-positive or screen-negative. An interpretive report is provided.
The Access AFP assay is a two-site immunoenzymatic sandwich assay. A sample is added to a reaction vessel with mouse monoclonal anti-AFP alkaline phosphatase conjugate and paramagnetic particles coated with a second mouse monoclonal anti-AFP antibody. The AFP in the sample binds to the immobilized monoclonal anti-AFP on the solid phase while, at the same time, the monoclonal anti-AFP-alkaline phosphatase conjugate reacts with different antigenic sites on the sample AFP. After incubation in a reaction vessel, materials bound to the solid phase are held in a magnetic field while unbound materials are washed away. Then the chemiluminescent substrate Lumi-Phos*530 is added to the reaction vessel and light generated by the reaction is measured with a luminometer. The light production is directly proportional to the amount of AFP in the sample. The amount of analyte in the sample is determined by means of a stored multi-point calibration curve.(Beckman-Coulter Assay Manual Beckman Coulter, Inc., Fullerton CA 2010)