Medical questions & health advice by licensed doctors
"How often are blood pregnancy tests wrong?"
I just got back the results of a blood pregnancy test I took at a local clinic, and according to these results, I am pregnant. What are the chances that this result is inaccurate?
Modern blood tests are not perfect but in general very good. A best type of physician to discuss a positive pregnancy test is an OBGYN. Pregnancy is detected by detecting a pregnancy specific hormone called human chorionic gonadotropin (HCG).
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A positive blood HCG means pregnancy more than 97% of the time. There are only a few exceptions to this. First the blood HCG test can detect very low HCG levels which can be a normal occurrence in some women. Most clinics have thresholds for a positive test that are much higher than these very low levels. Thus if the clinic told you it was positive, it was above the level which could be considered normal. Second, a gestational tumor know as a hydatidiform mole can produce a positive pregnancy test. A molar pregnancy results from an abnormal conception and produces a tumor. Another possibility is a very rare tumor called a choriocarcinoma which can produce HCG. These tumors are uncommon, but can present as a malignancy. I suggest that you schedule an appointment with your OBGYN. If you plan to keep the pregnancy, you will need to discuss prenatal care and things you should expect as you progress. I hope everything turns out well.
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