According to the American Pregnancy Association, a blood pregnancy test can detect pregnancy 7 to 12 days after conception occurs, while a urine pregnancy test can detect a pregnancy approximately two weeks after conception. For a blood pregnancy test, any HCG level greater than 25 milli-international units per milliliter is considered to be positive. The level of HCG required by a urine pregnancy test is anywhere from 25 to 100 milli-international units per milliliter.
A blood pregnancy test is the most sensitive type of pregnancy test and can detect a pregnancy much sooner than a urine pregnancy test. It can detect a tiny amount of human chorionic gonadotropin (HCG). HCG is produced after the fertilized egg implants. A woman can have a positive blood pregnancy test within a couple days after the embryo has implanted.
A urine pregnancy test requires higher levels of HCG in order to detect a pregnancy. Many doctors recommend waiting until a woman expects her menstrual period to test with a urine pregnancy test. This gives HCG levels a chance to build up to a detectable level, decreasing the chance that a woman receives a false negative result.