The home pregnancy test was positive but the blood test was negative. Why?
If your home pregnancy test was positive while a blood test was negative, first and foremost, you must take a second test to confirm whether or not you are pregnant. Home pregnancy tests are around 97% accurate when done correctly. However, a blood test is more accurate, but not necessarily more sensitive. The results depend a lot on the lab, methodology and technique of the blood test performed.
A positive result from a home pregnancy test shows the presence of the hormone human chorionic gonadotropin (hCG) in your system. This is usually a sign that you have become pregnant.
A quantitative blood test, usually called a beta human chorionic gonadotropin (hCG) test, measures the exact units of human chorionic gonadotropin (hCG) in the blood. That means it will detect even the most minimal level. There is another type of blood test sometimes called a qualitative human chorionic gonadotropin (hCG) test. This is a test that simply gives a yes or no answer to whether you are pregnant.
There could be various reasons why your home pregnancy test was positive while a blood test was negative. Just like home pregnancy tests, labs vary as to what is considered a positive pregnancy test. Common cutoffs for positive blood tests for pregnancy are 5, 10, and 25 units. A level under 5 is considered negative. A blood test that is only triggered at 25 units of human chorionic gonadotropin (hCG) is not any more sensitive than several of the home pregnancy tests.
Reasons for differing results:
Here are a few reasons why there was a discrepancy in your urine and blood test results:
1. False Positive
A false positive pregnancy test is when the test says that you are pregnant but actually you are not. Please read our article on false positive home pregnancy test results and what causes them, for more details.
2. Qualitative Pregnancy Blood test
This blood test may register as negative even though a woman is pregnant if the woman takes diuretic medications, or “fluid pills.” These drugs interfere with the test results. In addition, the test does not become positive until at least 7 to 10 days after a woman becomes pregnant. In most cases, by the time a woman misses her period the test will be positive if she is pregnant.
3. Quantitative Pregnancy Blood Test
In this test, lower-than-normal human chorionic gonadotropin (hCG) levels may be because of one of these reasons – ectopic pregnancy, a miscarriage, or abortion. The miscarriage may only be threatened and never happen, may be happening at the time of the test, or may have already occurred. Further testing can determine which of these the actual reason is. This test is also affected by the use of diuretics, or “water pills,” by the mother, which can interfere with the result. In addition, the test may fail to detect HCG even when a woman is pregnant if the test is done too early. It takes at least 7 days after fertilization for the test to become positive.