According to About.com, a blood pregnancy test can detect the levels of hCG and show a positive pregnancy result approximately 8 to 10 days after conception. HCG stands for human chorionic gonadotropin, which is a hormone secreted during pregnancy.
WebMD states that there are two types of blood pregnancy tests: the qualitative hCG test and the quantitative hCG test. A qualitative hCG simply provides a positive or a negative result, while a quantitative hCG gauges the exact levels of hCG in the blood. According to About.com, practitioners can monitor a pregnancy for miscarriage, ectopic pregnancy and the possibilities of multiples using serial blood tests.