According to Medical Health Tests, it takes between one and two days for a blood pregnancy test result to come back, depending on the individual physician's office and the laboratory used. Blood tests can detect a pregnancy within seven to 12 days from conception.
According to the American Pregnancy Association, a blood test detects pregnancy by measuring the concentration of the hormone hCG in a woman's blood, using either a qualitative or quantitative testing measure. Pregnancy blood tests are more accurate than urine home pregnancy tests, which have a 97 percent accuracy rate, according to WebMD. Quantitative hCG tests can also detect ectopic pregnancies.