After a missed period, it is possible to get a positive result on a pregnancy blood test as early as 7-12 days. However, the accuracy of the test may vary depending on factors such as the sensitivity of the test and the levels of hCG (human chorionic gonadotropin) in your body. Some tests claim to detect pregnancy even before your missed period, but it's generally recommended to wait until after you've missed your period for accurate results. If you suspect you might be pregnant, it's best to consult with your healthcare provider for guidance on when to take a blood test or perform other confirmatory tests.