Delayed for 2 weeks

Hi! Currently 2 weeks delayed ang partner ko and dapat Aug 15 meron na siya. We had sex on July 22 and Aug 19. Nag pt na siya noong Aug 20 (Negative) and Aug 29 ( 2 PT, Negative). Accurate na kaya ang blood test na sinasabi nila? Thank you! #pleasehelp #delayed #menstruation