Can Urine Pregnancy Test Be Positive While Blood Test Shows Negative?

Is it possible to have a negative pregnancy test after using an IUD and a blood test confirming no pregnancy?

My partner and I have been consistently using the Mirena IUD for contraception, without condoms or ejaculation.
However, recently after her period, my girlfriend has been feeling unwell (experiencing blood clots and spotting).
When she went to the gynecologist for a check-up, both her urine and a home pregnancy test showed positive results, although the test line was very faint.
A blood test has been scheduled for a few days later to confirm the results.
I would like to know if this could be related to the sexual intercourse we had during the fourth week after the IUD was removed.
I have also researched and found that if the IUD is used correctly, it is effective even during the week of removal.
Therefore, I would like to ask if it is possible to have a positive urine test while the blood test results could indicate no pregnancy?

Niming, 20~29 year old female. Ask Date: 2022/05/18

Dr. Zhang Kunmin reply Obstetrics and Gynecology

Hello, based on your description, if both tests are accurate, the results should be consistent.
I recommend waiting for the blood test report for confirmation.
Thank you! Wishing you peace and health.
Dr.
Chang

Reply Date: 2022/05/18

More Info

Yes, it is indeed possible for a urine pregnancy test to show a positive result while a blood test shows a negative result, although this scenario is relatively uncommon. The discrepancy between the two tests can arise from several factors, which I will explain in detail below.

First, let's understand how both tests work. Urine pregnancy tests detect the presence of human chorionic gonadotropin (hCG), a hormone produced shortly after a fertilized egg attaches to the uterine lining. Blood tests, on the other hand, can measure the exact level of hCG in the bloodstream and are generally more sensitive than urine tests. Blood tests can detect lower levels of hCG and can confirm pregnancy earlier than urine tests.

However, there are situations where a urine test may yield a positive result while a blood test does not. One possible explanation is the timing of the tests. If the urine test is taken shortly after implantation, hCG levels may be high enough to trigger a positive result in urine but not yet elevated enough to be detected in the blood. This is particularly relevant if the urine test is taken very early in the pregnancy, as hCG levels can vary significantly in the early stages.

Another factor to consider is the sensitivity of the urine test used. Some home pregnancy tests are less sensitive than others, meaning they may detect lower levels of hCG. If the urine test is sensitive enough to pick up a very low level of hCG, it might show a faint positive line, while the blood test, which is more quantitative, might return a negative result if the hCG level is below the threshold for detection.

Additionally, there are rare cases of biochemical pregnancies, where a fertilized egg implants and begins to produce hCG, but the pregnancy does not progress. In such cases, a urine test may show a positive result due to the presence of hCG, but subsequent blood tests may show low or undetectable levels of the hormone as the pregnancy fails to develop.

It is also important to consider the possibility of a false positive result from the urine test. This can occur due to various reasons, including the presence of certain medications or medical conditions that can interfere with the test results. For example, some fertility medications that contain hCG can lead to a false positive result on a urine test.

Given your situation, where your partner has been using a contraceptive device and has experienced unusual symptoms, it is essential to follow up with the healthcare provider for further evaluation. The fact that the urine test showed a faint positive line suggests that there may be some level of hCG present, but the negative blood test indicates that it is not at a level typically associated with a viable pregnancy.

In conclusion, while it is possible for a urine pregnancy test to be positive and a blood test to be negative, it is crucial to interpret these results in the context of the timing of the tests, the sensitivity of the tests used, and any underlying medical conditions. It is advisable to wait for the results of the blood test and consult with a healthcare professional for a comprehensive evaluation and guidance on the next steps. If there are ongoing symptoms or concerns, further testing, including repeat blood tests or ultrasounds, may be warranted to clarify the situation.

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