Accuracy of Blood Tests for Pregnancy
Question
Are blood tests 100% accurate when testing for pregnancy? Is it possible to take a blood test too early to detect HCG?
I took Provera March 29th which brought down my period on April 9th, which lasted 17 days. I haven’t had a period since, but I’ve had fatigue, nausea, and vomiting everyday for three weeks. I took a blood test that came out negative. I am also having a pink discharge sometimes after intercourse and after urination. Could I be pregnant?
Answer
Last Updated: June 14, 2013
The blood test performed to detect pregnancy evaluates the presence of a hormone called human chorionic gonadotropin (hCG).
This hormone is produced by the newly formed placenta associated with a pregnancy. It appears in the blood stream about the time of the implantation of the child into the uterus of its mother. This event (implantation) occurs about three to five days after ovulation and fertilization. hCG is therefore detectable in the blood about five to eight days after ovulation and fertilization. There is therefore about a week during which you are pregnant but may not have detectable levels of hCG in your blood stream–during this time, your blood pregnancy test would be negative. The urine pregnancy test also checks for hCG, but it is not as sensitive as the blood test–this turns positive about the time of one’s missed period (about two weeks after ovulation and fertilization.). Though it is therefore possible that you could be pregnant in the face of a negative blood pregnancy test, it would be unlikely that your symptoms are caused by an undetected pregnancy. If your pregnancy were far enough along such that your hormone levels (chiefly progesterone) were responsible for your symptoms (fatigue, nausea, vomiting), then a blood test should turn up detectable levels of hCG.
It could not hurt to repeat the blood or urine pregnancy test (the latter should be positive by now if you are pregnant). I would explore other reasons for your symptoms, though. In particular, the reason you needed provera in the first place to induce a period suggests that you may not be ovulating. If this is the case, you would not be producing your own progesterone, and this could make you feel lousy.
Your pink discharge after intercourse could be due to an inflammation of your cervix, which could be caused by an infection or inadequate progesterone. You should have a thorough evaluation by your doctor to get to the bottom of the problem.
Dr. John Gisla
This hormone is produced by the newly formed placenta associated with a pregnancy. It appears in the blood stream about the time of the implantation of the child into the uterus of its mother. This event (implantation) occurs about three to five days after ovulation and fertilization. hCG is therefore detectable in the blood about five to eight days after ovulation and fertilization. There is therefore about a week during which you are pregnant but may not have detectable levels of hCG in your blood stream–during this time, your blood pregnancy test would be negative. The urine pregnancy test also checks for hCG, but it is not as sensitive as the blood test–this turns positive about the time of one’s missed period (about two weeks after ovulation and fertilization.). Though it is therefore possible that you could be pregnant in the face of a negative blood pregnancy test, it would be unlikely that your symptoms are caused by an undetected pregnancy. If your pregnancy were far enough along such that your hormone levels (chiefly progesterone) were responsible for your symptoms (fatigue, nausea, vomiting), then a blood test should turn up detectable levels of hCG.
It could not hurt to repeat the blood or urine pregnancy test (the latter should be positive by now if you are pregnant). I would explore other reasons for your symptoms, though. In particular, the reason you needed provera in the first place to induce a period suggests that you may not be ovulating. If this is the case, you would not be producing your own progesterone, and this could make you feel lousy.
Your pink discharge after intercourse could be due to an inflammation of your cervix, which could be caused by an infection or inadequate progesterone. You should have a thorough evaluation by your doctor to get to the bottom of the problem.
Dr. John Gisla
Answered By:
John Gisla, MD
Dr. John Gisla, Board Certified by the American Academy of Family Physicians, pracitces in the Sacramento Region.
