Factors Affecting Home Pregnancy Tests

The accuracy of home pregnancy tests depends on several factors that can affect the results, giving a false negative or positive 3. Still, home pregnancy tests are around 97 percent accurate when used correctly 3. To confirm the results of a home pregnancy tests, see your doctor for an in-office urine test or a blood test that's sent out to a lab for the most accurate confirmation 3.

Determining HCG

Home pregnancy tests work by determining the amount of hCG, or human chorionic gonadotropin, in your urine 3. This hormone is produced when implantation occurs, which is when the fertilized egg attaches to the uterine wall. As the egg develops, the hormone levels increase. Home pregnancy tests usually detect hCG levels after about two weeks, but that can vary depending on the sensitivity of the test 35. HCG levels rise dramatically in the first few weeks of pregnancy; more than doubling every two days, so home pregnancy tests are more accurate the further along you are 35. HCG levels tend to begin to decrease between weeks 10 and 12 of the pregnancy 5.

Timing It Right

Testing too early in your cycle can result in a false negative because you might be pregnant without having high enough hCG levels to register a positive result on the test 5. For the most accurate results, it's best to wait until you miss your period before taking a home pregnancy test, or even a few days after. Take the test first thing in the morning when the hormone is the most concentrated in your urine for the best chance of the home pregnancy test recognizing hCG levels 5.

Taking It Correctly

Sometimes a home pregnancy test isn't accurate because the user did not carefully read the directions. Follow the directions carefully, and check the expiration date on the test -- home pregnancy tests expire and may not provide accurate results after their expiration dates 3.

Also, consider what medications you are taking. Some fertility drugs contain hCG, and other medications, including some tranquilizers and diuretics, act like hCG, according to the Mayo Clinic 123. These drugs can fool home pregnancy tests into returning a false positive result 3.

Areas of Concern

Rarely, serious illness such as some types of cancer can lead to a false positive on a pregnancy test. In addition, an ectopic pregnancy or miscarriage can cause a positive as well, even though the pregnancy isn't viable 4. If you are unsure of the accuracy of your home pregnancy test results, visit a doctor for a blood test. Blood tests are more sensitive and more accurate.