Some Information About How Home Pregnancy Tests Work, And How To Make Sure You Get The Most Accurate
After conception, the hormone hCG (human chorionic gonadotropin) is produced by the placenta and may be found in the blood and urine. Home pregnancy tests are used on urine samples.
According to Hulisz and Urbanski [U.S. Pharmacist, 21(3), 1996], home pregnancy tests work by using substances -- monoclonal or polyclonal antibodies in an enzyme-linked immunoassay -- that bind to the hCG. If HCG is present in the urine sample, it will be trapped by the anti-hCG antibody that is bound to a solid surface.
In the case of OTC (over the counter) pregnancy tests, this generally takes
the form of a stick or filter. A second antibody is used to react with
the anti-HCG complex, causing a color change and producing what appears
as a positive result.
When should I test? Any special tips on how to test?
You should wait at least until the day your period was due, 14 days after ovulation -- which is usually somewhere between 26-36 days after the first day of your last regular period. Some pregnancy tests require you test only first morning urine. This is because first morning urine tends to be stronger, and contains more of the hCG hormone. The greater the concentration of hormone, the easier it is for the kit to detect.
For best results, carefully read the directions on each individual test, as instructions may vary -- and accuracy depends on you following the directions
precisely. If there are terms you don't understand, look them up or contact
the manufacturer -- most provide toll-free numbers. In general, be sure
to store the test at room temperature, make sure the test has not expired,
and do not open the inner package (containing the test device) until you
are ready to test. When testing, make sure you wet the appropriate area
thoroughly -- placing it in the stream of urine for at least five seconds
is generally recommended. After you wet the stick, most tests require that
you place the test on a flat surface while you wait for the result.