A pregnancy hcg test checks for the presence of the pregnancy hormone hCG or human chorionic gonadotropin in your body. A false positive hCG pregnancy test, a positive hCG test when you are not pregnant, rarely happens, but if it happens then it can be seen both with blood and urine tests, though in each case, the causes can be slightly different.
False positive versus false negative pregnancy test
- A false positive pregnancy test means that your pregnancy test is positive but you are NOT pregnant.
- A false negative pregnancy test means that you test negative but you ARE pregnant.
- A true positive pregnancy test means that your pregnancy test is positive and you are pregnant.
- A true negative pregnancy test means that your pregnancy test is negative and you are NOT pregnant.
The urine pregnancy test checks for the presence of the pregnancy hormone hCG human chorionic gonadotropin. hCG made by the placenta which exists only in pregnancy. A positive test that was done correctly has a 99% reliability that you are pregnant. A positive pregnancy test usually means that you are pregnant. There are only a very few circumstances in which a positive pregnancy test means that you are not pregnant (False Positive Test).
False positive urine tests can also occur under the following circumstances:
- Fertility treatment: If you receive shots of hCG or gonadotropins (for example, Pregynl, Profasi, Pergonal, APL) for ovulation it's posible to have a positive urine or blood pregnancy test for two to three weeks after the shot and not be pregnant. A rising blood hCG level usually indicates a pregnancy. This is what happened to Kim Kardashian.
- Evaporation line. If you read the test after the suggested time has passed.
- Improper Testing - When taking a home pregnancy test, it is very important to read the directions before testing. Your home pregnancy test instructions will specify when test results should be interpreted and when test results are no longer valid. Some tests will produce a faint positive test result if read after the instructed time. You should use a clock or a watch and record the time you perform the test and read results at the instructed time. Guessing how long it has been since performing the test can lead to false results. Three minutes can seem like twenty minutes and vice versa when you are anxiously waiting to find out if you are expecting.
- Chemical pregnancy - This is a pregnancy that has a positive pregnancy test but the embryo or fetus do not develop
- Very early pregnancy loss or miscarriage
- Certain rare medical conditions such as gestational trophoblastic disease, pancreas islet-cell tumors, adenomyosis, gonadoblastoma, bladder cancer, lung cancer, after blood tranfusion.
- Medications - Some drugs like Methadone, chlordiazepoxide, or promethazine can give a false positive pregnancy test
- "Phantom-hCG" The most important though very rare false positive blood test is a woman who has a low positive blood pregnancy test, the urine test is negative, and she is not pregnant.
- Menopause: Some women age 50 and older in menopause may have a slightly elevated blood hCG test, which usually is not associated with a pregnancy.
- Defective Pregnancy Test - Expired tests or faulty home pregnancy tests can also lead to false positive results. Always check the expiration date before testing to assure accurate results. Keep in mind, even with the highest quality control, an occasional defective test may occur.
If you have tested positive and are unsure about the results of your home pregnancy test, consult your doctor.
What Is A Phantom hCG And What Causes the False Positive Pregnancy Test
A "Phantom hCG" is a positive blood pregnancy test without being pregnant. Patients with a phantom hCG will have a persistently and not significantly rising positive blood pregnancy test but the urine test is negative.
Phantom hCG and phantom choriocarcinoma syndrome (pseudohypergonadotropinemia) refer to persistent mild elevations of hCG, leading physicians to treat patients with cytotoxic chemotherapy for choriocarcinoma when in reality no true hCG or trophoblast disease is present.
The hCG test, or pregnancy test, is one of the most common tests done in laboratories. It is assumed that an hCG assay detects only hCG or hCGß. This is not always the case. hCG kits can detect a wide and varying range of different hCG-related molecules in serum or urine samples.
- hCG dissociation and degradation products, like the free ß-subunit, nicked hCG and
- ß-subunit core fragment
- hyperglycosylated hCG a variant of hCG with separate biological functions and
- a pituitary gland-produced variant of hCG
The reason for a phantom hCG is that some individuals react falsely positive to some substrate in the blood hCG test and thus they will display a consistently low positive blood pregnancy test even though they are not pregnant, but their urine test will be negative. This phantom hCG may lead to serious misdiagnosis and intervention, but can be detected with serial dilutions. Patients with phantom hCG have a positive blood hCG but a negative urine hCG test. Therefore, if there is a question, a urine test should be done together with the blood hCG test.