Quantitive blood pregnancy test came back negative two weeks after missed period. how accurate is it? should i still be worried about pregnancy?

Very accurate: The home urine pregnancy tests are also very accurate at 2 weeks after an expected period. Negative means not pregnant as of 2-3 weeks ago, but probably means not pregnant as of 1.5-2 weeks ago with these sensitive tests. So, if still having sex over the past 1.5-2 weeks, there is a chance of a brand new conception that is too early to cause a positive test result.