The most common test used after infection with a novel coronavirus is nucleic acid testing. The most commonly used specimen for nucleic acid testing is a throat swab test, which is also the easiest to obtain. It is usually 3-5 days after infection that an infected person may be detected by a throat swab, but this is when the viral load is relatively low and false negatives are possible. If symptoms are more supportive, another retest will also be recommended, and if it remains negative both times for more than 7 days, it can be ruled out. Serum antibody tests, including IgM and IgG, have now been developed, and in the 7th edition of the novel coronavirus pneumonia protocol, a throat swab and serum antibody test are recommended for suspected cases. If both meet negative, especially after more than 1 week of illness, the antibodies are still negative and can be considered excluded. So both are now the most commonly used tests. In addition, if there is a high degree of clinical support for novel coronavirus pneumonia, but the throat swab is negative for nucleic acid, deep respiratory secretion testing, such as sputum and alveolar lavage fluid testing, will also be recommended. For discharged patients, some hospitals recommend stool nucleic acid testing, and only allow the patient to be discharged if it is also negative. Source: Dr. Yurai