While I was at the pharmacy the other day, I had a patient approach me with some concern about her pregnancy test. Apparently her test told her she was pregnant while the blood test at her doctor's office said she was not! Home pregnancy tests (HPT) are 97% accurate so how in the world could a patient end up with a positive result on the HPT, but get a negative outcome at her doctor's office (this is called a false positive)?

First, a little background on the home pregnancy tests! Home pregnancy tests are built to detect the hormone called human chorionic gonadotropin (HCG) in the urine. HCG is produced by the placenta, and the placenta is made when the fertilized egg attaches to the lining of the uterus (implantation). The whole implantation process takes place between 5 to 10 days after the egg becomes fertilized. This means the home pregnancy test will not be able to detect a pregnancy until at least 5 days after the sperm has fertilized the egg.

A false positive may occur if the patient:

1) let the test sit for too long.
2) had a urinary tract infection (UTI) caused by a specific bacteria.
3) had been taking certain drugs like HCG shots for infertility treatment, anti-convulsants, certain diuretics, and certain drugs to treat Parkinson's disease.
4) caught the pregnancy early, but she ended up going on to have her period due to early miscarriage.

Home pregnancy tests are fast, easy to perform, and very accurate when used correctly. If you come up with positive results, please be sure to follow-up with your doctor as soon as you can!