Blood Test Results:
Blood tests performed at a doctor’s office tend to have a 98 to 99 percent accuracy rate. These tests can be conducted seven days after you ovulate (which is about a week before your period is due) and still provide accurate results.
As with urine pregnancy tests, it is possible to end up with false results (both negative and positive) from a blood pregnancy test.
•False negative results (test is negative, but you are actually pregnant) usually occur if the test was performed too early. This is because there may not be enough hCG in the blood to detect a pregnancy.
•False positive results (test is positive, but you are not pregnant) may appear if you are taking a medication that contains hCG.
at 2:38 AM on Oct. 31, 2010