February 25, 2020 | By Heidi Tian
At home urine pregnancy tests are the most convenient and widely used tool to find out if you are pregnant. They work by detecting human chorionic gonadotropin (hCG), which is a hormone produced during early pregnancy.
Unfortunately, you may occasionally receive a false positive pregnancy test result. We would like to share with you the most common causes to help you be more confident when interpreting your test results.
1. Evaporation Lines
If a pregnancy test is left out for longer than the recommended read time, there may be a slight T line discoloration called an "evaporation line", which resembles a positive pregnancy test. It is critical for users to follow the instructions exactly while taking the test.
2. Chemical Pregnancy
A chemical pregnancy occurs if a fertilized egg, known as the embryo, is unable to implant or grow. This can happen for a wide range of reasons, such as fibroids, scar tissue, low progesterone, or a congenital uterine anomaly that causes an irregularly shaped uterus.
3. Recent Miscarriage or Abortion
After an abortion or miscarriage, the level of hCG starts to decrease, but very slowly. Typically, hCG declines over a period ranging anywhere from 9 to 35 days. The average time frame is around 19 days. Taking a pregnancy test within that period can result in a false-positive test.
If you’re undergoing fertility treatment, your doctor may prescribe a synthetic hCG trigger shot under brand names like Novarel, Pregnyl, Pergonal, Ovidrel, or Profasi, which helps follicles release mature eggs. Unfortunately, these can also lead to a false positive result.
Other medication that can cause a false positive result include -- but are not limited to:
- anti-anxiety medications, like diazepam (Valium) or alprazolam (Xanax)
- antipsychotics, such as clozapine or chlorpromazine
- antihistamines, including promethazine
- anticonvulsants, like phenobarbital or other barbiturates
- Parkinson’s disease medications, including bromocriptine (Parlodel)
- diuretics, like furosemide (Lasix, Diuscreen)
- methadone (Dolophine)
5. Medical Conditions
Certain medical conditions can cause a woman’s hCG level to increase and trigger a positive result while she is not pregnant. These include, but are not limited to:
- disorders affecting the pituitary gland and hormone levels, specifically in perimenopausal women
- gestational trophoblastic diseases, which cause tumors in the cells that would normally make up the placenta
- ovarian cysts, particularly corpus luteum cysts
- ectopic pregnancy
- phantom hCG, where antibodies interfere with the testing kit
- sulfated hCG, most commonly seen in perimenopause
- urinary tract infections
- in very rare case, cancers of the bladder, cervix, colorectal region, endometrium, lungs, ovaries, pancreas, kidneys, liver, breasts, and stomach
You may wonder how to distinguish a false positive from a true one. It is easier than you'd think. Keep taking tests every few days. If the T line gets darker, then you are likely seeing the doubling of the hCG hormone levels, which occurs with early pregnancy. If not, you may be getting a false positive.
A positive at-home pregnancy test result should always be followed up with a doctor’s appointment. Your doctor may give you a blood or urine test to confirm the results and monitor your hCG levels. If you’ve received a false positive, your doctor’s visit will determine that, too.
Remember that false positives do happen but they are not a sign you’ll never get pregnant. Have faith and keep testing!