Blood tests cannot detect whether the body is infected with novel coronavirus. After a novel coronavirus infects the human body, in addition to symptoms such as fever and malaise, patients usually have some changes in blood routine, such as normal or reduced total white blood cell count and reduced total lymphocyte count, although these changes are not characteristic and are very similar to those caused by other viral infections, so they are not sufficient as a basis for diagnosis. At present, the diagnosis of novel coronavirus relies mainly on the results of pathogenic tests, and before doing the tests, it is necessary to determine whether a person is suspected of having the virus. The identification of a suspected virus-infected person requires a combination of epidemiological history, clinical manifestations, chest X-ray (or CT), and routine blood test results, and if they are consistent, they can be established and subsequent pathogenic testing can be performed.