pregnancy testing

• What do pregnancy tests detect?

  the hormone hCG that is found in the urine of pregnanct women
• what is hCG?

  Human chorionic gonadotropin
• what does the application area contain?

  antibodies for hCG bound to a blue coloured bead
• what happens when urine is applied to the application area?

  any hCG will bind to the antibody on the beads, forming an antigen-antibody complex

  the urine moves up the stick to the test strip, carrying any blue beads with it
• what does the test strip contain?


  Antibodies to hCG that are stuck in place (immobilised)
• what happens if there is hCG present?


  • Test strip turns blue ...
  • ...Because the immobilised antibody binds to any hCG - concentrating the hCG-antibody complex with the blue beads attached
• what happens if no hCG present?

  the beads will pass through the test area without binding to anything, and so it won't go blue