How long does it take for a blood test to detect pregnancy?

I called the lab at the hospital near me who does these bvlood test the person Ispoke with told me that if you take a blod test to early it will show up neg. you need to wait at least 1 week past when you were expected to start ovualation, it will not show a pos. if you are until implantation has taken place so if you chart your cycles and know when you ovulate then you can have one done with pretty much accrute results 7-10 days after that.sometimes sooner but for best results 7-10days