New crown antigen test results are generally judged to be invalid after more than 30 minutes. The new crown antigen test can generally be read in about 15 minutes, from which it can be analyzed as positive or negative, but if it is observed again after more than 30 minutes, there is no significance of any judgment, and the antigen test results will change after being left for a long time, so it cannot be used as a test standard. If you take a picture with your cell phone about 15 minutes after the antigen test, you can take another picture about 20 minutes after the test, and then compare the results of the two tests; if the results of the two tests are the same, it can be used as a standard test. After the antigen test, it is necessary to pay attention to observation, if there is a dark and a light, or both lines are red, you should inform the doctor as soon as possible to improve the nucleic acid test.