How early can a blood test detect pregnancy?

I’m about 2 weeks late & I’ve taken several home pregnancy tests, but all negatives. How early can a blood test detect pregnancy as opposed to an HPT?

When do the home pregnancy tests become effective and am i prego ?

My boyfriend of 2 years and I had unprotected sex and we’re afraid of the precum. I’m suppose to have my period in about 3 days, so will the home pregnancy tests work?