Is it possible for a pregnancy test result to be false positive? The answer is a resounding “Yes”, though the chances to see a wrong positive pregnancy test result are very slim. It is rarely seen. But, there are quite a few reasons that can cause such results.
What are false positive pregnancy tests?
A false positive pregnancy test result is a positive result of the test telling you that you are pregnant when in fact, you are not.
Although pregnancy blood tests claim 99% accuracy and home pregnancy tests have an accuracy rate of 97%, you could get a false positive pregnancy test result with both types of tests. This can be due to certain factors.
99 percent accuracy means one out of hundred tests can be wrong. Similarly, 97 percent accuracy means 3 out of 100 test results can be wrong.
It could also be that, you were pregnant when you tested positive but, then you aborted early or had an early miscarriage. This is called chemical pregnancy and the bleeding period that follows is a bit heavy. In this case, the result was correct but you lost the pregnancy later.
How do pregnancy tests detect pregnancy?
When you conceive, the fertilized egg travels down to the uterus within 6 to 8 days. It then implants itself firmly on the uterine wall and begins to grow.
The placenta then forms immediately after implantation and starts secreting the Human Chorionic Gonadotropin hormone (hCG), which rapidly goes on doubling every 72 hours in the blood throughout the first trimester. It is also found present in the urine.
The blood pregnancy test and the home pregnancy test basically determine pregnancy by detecting the hCG in blood and urine.
The presence of hCG can be detected in the mother’s blood 24-48 hours after implantation. It can be found in her urine just a few days later.
According to the American Pregnancy Association, a blood pregnancy test can detect hCG about 11 days after conception, while a urine test can detect it 12 to 14 days after conception.
Reasons that cause false positive pregnancy test results
Looking at most of the reasons that cause a wrong positive report, you will see that you cannot blame the testing kit for the false report. It is supposed to detect the hCG, which it rightly does.
The causes are mostly those that raise your hCG levels such as certain medications, some health conditions, or the wrong technique of doing the test.
Let us look at the various reasons that can cause a false pregnancy test result.
A false positive test can happen when the test has detected the presence of Human Chorionic Gonadotropin hormone (hCG) in blood/urine and which it is supposed to do.
These detectable levels of hCG in blood or urine could have been produced by certain medications you may be taking such as hCG-containing fertility drugs or injections to induce ovulation (except Clomid), promethazine (antihistamine), hypnotics like Ambien, etc.
Then, there are certain weight loss experts who advise hCG shots for weight loss purposes. This is not approved by the FDA, though the shots are legal and approved for fertility problems.
However, commonly used drugs like antibiotics, painkillers, or even birth control pills do not affect the result of the test.
Another common cause of a false positive result is improper doing of the test or wrong interpretation of the results.
The results of the test should be read at the interval specified by the manufacturer, which is usually five minutes or slightly less or more. Any delay in reading the test result can give a false positive result.
Evaporation lines may be seen on many home pregnancy tests if read after the suggested 3–5 minute window or reaction time.
Check out the stats: A review has shown that home pregnancy tests are accurate to the extent of 97% when performed by technicians but the accuracy drops down to 75% when done by non-expert users.
Basically, wrong techniques of doing the test are one of the contributory factors.
Certain medical conditions
Certain medical conditions, which increase hCG levels in the blood can cause a false positive pregnancy test. Here, though the test report is correct in giving the positive result because it has detected the hCG, you are not pregnant. Such conditions include:
- Choriocarcinoma (a rare cancer of the uterus)
- Certain types of breast and ovarian cancers
- Some diseases of the liver
- Pituitary tumors
- Testicular cancer can give a false positive result in men
Corpus luteum cysts present in the ovaries can give false positive results on pregnancy tests.
The corpus luteum is the part of the follicle that remains in the ovaries after the egg is released from it. Normally it disintegrates with time.
But, if it fills with fluid or blood, it forms a cyst. Such as cyst does not disintegrate but stays on. The corpus luteum cyst produces the hCG hormone and therefore, can cause a false positive.
Some women develop multiple cysts. Such a condition is called polycystic ovarian syndrome. This can cause fertility issues.
Expired or defective pregnancy kits can also give false positive test results. This is probably the most common cause of a false positive pregnancy test.
After the expiry date, the potency of the chemical that detects the hCG hormone decreases and is no more sensitive to react with hCG. It does not react and give the correct result.
You can have a positive pregnancy test result, which can later turn negative at subsequent testing. This could be due to an early miscarriage or abortion.
This is called chemical pregnancy. You could test positive for a few days or even weeks after you have had a miscarriage.
According to the American Pregnancy Association, the reason for this is that the hCG levels in the blood can linger for weeks. After the miscarriage, remnants of the placenta can stay in the uterus and produce hCG, which can go on giving a false positive result.
Urine that contains blood, not necessarily of your period but from the urinary tract due to infection, and in addition protein, can give a false positive test result. This can happen due to kidney (nephritis) or bladder (cystitis) infection.
HCG is a glycoprotein comprising of amino acids and that is why the urine that has protein and/or blood can give a wrong positive result.
Detergent residue in the urine container can also cause a false positive.
Drugs that increase hCG levels in the blood and give false positive results
Drugs that can increase hCG levels in the blood include:
- Fertility drugs, which contain hCG
- Hypnotics like Ambien
- Promethazine – an antihistamine used in treating colds and allergies. It can also give a false positive pregnancy test
- Medicines used in the treatment of epilepsy
- Medications used in treating Parkinson’s disease
- Phenothiazines like chlorpromazine used to treat nausea and vomiting among other uses
- Certain prescription drugs contain hCG such as A.P.L., Novarel, Pregnyl, Profasi, and Ovarel which are drugs given to increase fertility in women and men.
It is, therefore, advisable to always confirm a home pregnancy test result by talking to your doctor and following it up with a pregnancy blood test.
You could also read missed period and false negative pregnancy test.