New Crown Antigen test over time and then appear a bar may be caused by error, need to be read within the specified time. The new crown antigen test paper test also has a certain validity time, if too long before the results of the judgment will be biased. If there is an extra bar on the test strip after the time has passed, it is possible that the test strip has oxidized from exposure to air. It is recommended to be on the safe side, this situation should still pay attention to exclude the possibility of infection with the new crown, you should go to the hospital to do a new crown virus nucleic acid test, to exclude the new crown virus infection. New crown antigen test is usually home self-testing, it is recommended to follow the instructions for standardized operation and interpretation.