Pregnancy Test 99% Accurate?

    Q: What does it mean when manufacturers claim their home pregnancy test HPT is 99% accurate?

    A: Manufacturers of home pregnancy tests (HPT) often claim their tests have a 99% accuracy but they frequently do not explain exactly what it means.

    It has nothing to do with how likely your pregnancy test will be positive when you miss your period or whether a negative test means you are not pregnant.

    The reason for this strange product claim relates to an arcane and old-fashioned Food and Drug Administration (FDA) regulation related to a comparison of the test in urine with added hCG in the laboratory.

    The manufacturer needs only to demonstrate that its test results, the result of a home pregnancy test, and using a nonpregnant woman's urine supplemented
    with commercial hCG, agree with those of an existing test more than 99% of the time. So 99% means how likely is it that the home pregnancy test made by this manufactures shows a positive results when it's testing a nonpregnant woman's urine mixed with a certain amount of hCG.

    With todays' products which are more sensitive than previous ones you would expect the HPT to be positive in the laboratory when it tests an artificially pregnant urine.
    But the 99% sensitivity has little to do with the actual urine or the question whether it will be positive early on.

    From: First Response Pregnancy Test:
    "FIRST RESPONSE® is over 99% accurate at detecting typical pregnancy hormone levels from the day of your expected period.2"
    "2 However, some pregnant women may not have detectable amounts of pregnancy hormone in their urine on the first day of the missed period or may have miscalculated the first day of their period."

    From: ClearBlue Easy Digital Pregnancy Test
    "The test is over 99% accurate from the day of your expected period†"
    "The Clearblue Easy Digital Pregnancy Test gives you results 5 days sooner‡
    99% accurate at detecting typical hormone levels. Note that hormone levels vary. See product insert."
    "The Clearblue Easy Pregnancy Test is over 99% accurate from the day of your expected period†"
    "The Clearblue Easy Digital Pregnancy Test gives you results 4 days sooner‡"

    † 99% accurate at detecting typical hormone levels. Note that hormone levels vary. See product insert.
    ‡ Clearblue Easy can be used as early at 4 days before you expect your period. That's 5 days sooner than waiting until you miss your period to test. The amount of pregnancy hormone increases rapidly in early pregnancy. In clinical testing with early pregnancy samples, Clearblue Easy gave the following results. 51% of pregnant women get results 5 days sooner. 82% get results 4 days sooner. 90% get results 3 days sooner, 95% get results 2 days sooner.
    ‡ Clearblue Easy can be used as early at 3 days before you expect your period. That's 4 days sooner than waiting until you miss your period to test. The amount of pregnancy hormone increases rapidly in early pregnancy. In clinical testing with early pregnancy samples, Clearblue Easy gave the following results. 55% of pregnant women get results 4 days sooner. 87% get results 3 days sooner. 92% get results 2 days sooner.