To get a truly accurate result it is best to do a laboratory blood test versus a home urine test. The blood test is more accurate and can detect pregnancy much earlier than a home test. Some home pregnancy tests are sensitive enough to detect a pregnancy 14 days after, however most are not and further are more likely to give a negative or a false positive.
A study published in 2004 in the American Journal of Obstetrics and Gynecology has shown that this is misleading for home pregnancy tests to claim that they are 99% accurate. The study evaluated 18 home tests and showed that only 1 was sensitive enough to detect the HCG levels on most women the day of their first missed period. The other tests were only able to pick up 16% of the pregnancy results accurately.
The FDA allows the claim because they perform better than existing tests 99% of the time. However, existing tests were much less accurate. To be sure, getting a clinical blood test is the best way to be sure.