pregnancy test

• Pregnancy tests use monoclonal antibodies to detect the presence of the HCG chemicals.

  
• So by urinating on the test strip (the orange beer to the end):

  The test can tell someone whether there’s HCG in their urine and that they’re pregnant.

  As the fluid travels up the absorbent fibres, it will cross three separate zones:

  1. The reaction zone
  2. the test zone
  3. The control zone

  
• How pregnancy test works - On the testing strip, without the plastic casting:

  The strip has two sides:

  • The reaction zone (left side) - with beads covered in monoclonal antibodies.
  • The test zone (right side) - with a bunch of monoclonal antibodies

  
• The test zone in the pregnancy test:


  • A bunch of monoclonal antibodies that specifically binds to HCG, if they come into contact with it.
  • The antibodies are fixed to the test strip, so they can't move.

  
• The reaction zone in pregnancy tests: 


  • The part where urine is applied.
  • Contains monoclonal antibodies that will specifically grab onto any HCG.
  • Attached to the antibodies is an enzyme with the ability to turn on dye molecules and are completely free to move around.
  • They’re not fixed to the strip.
  • The urine picks up all the antibodies with enzymes and carries them to the test zone, which is where the results show up.

  
• Pregnancy tests, when you're not pregnant:

  • If you wee on the strip, the urine will wash the unfixed beads along the test strip.
  • They’ll flow over the fixed antibodies on the other part and nothing will happen.
  • There's no HCG for the antibodies to bind to.
  • The test strip doesn't appear.

  
• Pregnancy test - when you're pregnant:

  • Your urine contains HCG then that will bind to the antibodies with enzymes.
  • Then they flow over the test strip:
  • The HCG that they’re carrying, binds to the fixed antibodies in the test zone as well.
  • Allowing the attached dye-activation enzyme to do its job and create a visible pattern.
  • The entire strip appears that indicates a positive test result.

  
• • Most pregnancy tests have two lines, rather than one.
  • The second line acting as a control, so you normally need two lines for a positive result.

  
• Human chorionic gonadotropin (HCG)


  produced by pregnant people, which is made by the very early embryo and the placenta.

  • It tells the body to not shed the inner lining of the uterus that month.
  • It supports the formation of the placenta, which transfers nutrients from mother to foetus.

  It's excreted in their urine.

  
• The control zone in pregnancy tests:


  This confirms that the test is working properly:

  • Whether the Antibodies with enzymes never saw the HCG or they’re extras because the reaction zone is overstocked with them.
  • All the unbound antibodies with enzymes, picked up in the reaction zone should end in the control zone and activate more dye for a strip.

  So if no pattern appears, then the test was faulty.

  
• False negatives can occur in pregnancy test:


  • If concentrations of HCG aren’t high enough for detection.
  • Don't test pregnancy right away, as HCG levels double every two to three days, so it may just be too early to tell.
  • Beverages can dilute the urine sample, so doctors recommend taking the test first thing in the morning.
• False positives can come from other sources of HCG like:


  • IVF injections
  • Ectopic pregnancies 
  • Certain cancers like uterine cancer or testicular cancer
• The purpose of the result window on a pregnancy test:


  It displays the result, showing if you are pregnant or not.
• The purpose of the control window on a pregnancy test:


  It shows if the test is working or not.