A blood pregnancy test usually becomes positive within 3-4 days after implantation, or several days before your expected menstrual period, when hCG levels have reached a high enough level.
The blood pregnancy test becomes usually positive about 10-11 days after ovulation and fertilization.
Typical pregnancy symptoms usually do not show up until after the blood hCG has reached significant enough levels.
An hCG level below 5 mIU/ml is considered negative, and a level above 25 mIU/ml is positive. You can't be sure that a blood hCG level between 5 and 25 mIU means it's a positive test because an hCG level between 5 and 25 mIU is considered 'equivocal,' which means we don't know if it's negative or positive.
At a blood hCG level between 5 and 25, most doctors probably repeat the test 2-3 days later. A rise above 25 mIU means that you are pregnant.