A bar of antigen generally refers to a bar of new coronavirus antigen, which is not necessarily OK, and its possible situations are: negative, invalid test, false negative and so on. 1. Negative: If the test is performed according to the correct operation method using a qualified kit, and the result is only a red bar at the control line, it generally indicates that the antigen test is negative. However, the antigen test cannot be taken as the final diagnostic result, and the diagnosis should be further clarified by nucleic acid test. 2. Invalid test: If after the test, there is no red bar on the control line, but only a red bar on the detection line, it means that the test result is invalid, which does not mean that there is no problem. It is necessary to re-test. 3. False Negative: Certain incorrect operations, such as unqualified specimens, unqualified reagent kits, reading the results of too long or too short a period of time, etc., will affect the correctness of the test results, the appearance of a bar. This situation does not indicate that there is no problem. It is necessary to take the correct test steps and use qualified kits to re-perform the test. In the case of a bar of antigen, if there are invalid tests and false negatives, it is important to retest using the correct test method and qualified kits. If necessary, seek medical attention for a definitive diagnosis by means of nucleic acid testing.