Pregnancy Testing

• Human embryo in uterus lining secretes a small hormone called human chorionic gonadotrophin (hCG), it is small so filtered out of blood plasma by kidneys (into Bowmans capsule) and is found in urine within 6 days of conception
• Presence of hCG in urine is basis of the pregnancy test, they contain monoclonal antibodies specific to hCG antigen (have complementary shapes)
• Small volume of urine is pipetted onto test strip section (‘sample’), at sample position, hCG molecules (antigen) bind to mobile monoclonal antibodies
• Antibody-hCG complex moves up strip with urine, until it binds to band of immobilised antibodies at ‘test’ point on strip, which is attached to a pink or blue dye
• Mobile antibody from ‘sample’ position will move with urine, up test strip even if not bound to hCG antigen, so will bind to immobilised antibody at ‘control’ position forming pink/blue line
• There is always one coloured control line, if urine has hCG, there will be two coloured lines on the test strip; positive pregnancy test