The assay is an immunometric ('sandwich') EIA for the quantitative
measurement of hCG in human serum or plasma and for qualitative urine
pregnancy testing. Sample hCG is bound by 2 monoclonal anti-hCG
antibodies directed at different epitopes. One antibody is attached to
magnetic particles and the other is labelled with alkaline phosphatase.
The assay has four main stages:
Magnetic anti-hCG is incubated with sample (100 µL) for 15
minutes at 37°C followed by 2 magnetic wash steps.
The magnetic particles are incubated with alkaline
phophatase labelled anti-hCG for 1 hour at 37°C followed by 2
magnetic wash steps.
A coloured enzyme substrate is incubated with the particles for
30 minutes at 37°C. The presence of alkaline phosphatase causes
a colour change from yellow to pink.
The reaction is terminated by addition of Stop Buffer.
The tubes are then placed in the spectrophotometer or colorimeter.
The optical density (at
550nm or 492nm) of each tube can be measured and the results
calculated using a data
processing program.