Why increasing antigen detection is conducive to "early detection"? Why can't it replace nucleic acid detection? Authoritative experts responded
2022-03-15
Strictly implement various measures for epidemic prevention and control! The comprehensive group of the joint prevention and control mechanism of the State Council recently decided to add antigen detection as a supplement on the basis of nucleic acid detection. People can buy antigen detection reagents for detection by themselves. Why increasing antigen detection is conducive to "early detection"? Why can't it replace nucleic acid detection? Li Jinming, deputy director of the National Health Inspection Center, was interviewed by Xinhua news agency. Why increase antigen detection? Conducive to "early discovery" Li Jinming introduced that COVID-19 mainly had 4 structural proteins, usually using N protein with high expression level as a target for antigen detection. Compared with nucleic acid detection, antigen detection is faster and more convenient. Some reagents can give results in 15 minutes. "To carry out epidemic prevention and control faster and more accurately, we need to add antigen detection as a supplement." Li Jinming said that isolation observers, including those in home isolation observation, close contact and secondary close contact, entry isolation observation, sealing and control areas, can pass the antigen detection once a day without leaving home, so as to find out the infected person as soon as possible while greatly saving human and material resources. According to the COVID-19 antigen detection application plan (Trial), the positive antigen results can be used for the early shunt and rapid management of suspected people, but not as the basis for the diagnosis of COVID-19 infection. "Once the antigen test is positive, it should be confirmed by nucleic acid test in time, that is, 'antigen screening and nucleic acid diagnosis', which is conducive to' early detection 'and improve the sensitivity of monitoring and early warning." Li Jinming said. Why can't it replace nucleic acid detection? Or missed or false detection According to the latest plan, nucleic acid detection is still the basis for the diagnosis of COVID-19 infection. As a supplementary means, antigen detection can not replace nucleic acid detection. The reason is that the sensitivity of antigen detection is relatively low. Usually, antigen detection products can be detected only when the infected person is in the stage of acute infection, that is, the viral load in the body is at a high level. Li Jinming introduced that compared with nucleic acid detection, antigen detection has poor sensitivity because there is no amplification process. Generally speaking, it shortens the time to produce results, but increases the risk of "false negative". "Especially when the infection time is long and the virus load becomes low, missed detection may occur." In addition, the specificity of antigen detection is also weaker than that of nucleic acid detection, that is, it is more prone to false positive false detection. "In the population with low epidemic rate, the number of 'false positive' may even far exceed the number of 'true positive'." Li Jinming said that this is also an important reason why our country adheres to nucleic acid detection as the basis for the diagnosis of COVID-19 infection. According to the above scheme, if the grass-roots medical and health institutions have the ability of nucleic acid detection, nucleic acid detection shall be the first choice; Those who do not have the ability of nucleic acid detection can carry out antigen detection. Which groups apply? It is expected to screen asymptomatic infections According to the plan, community residents who need self-test can purchase antigen test reagents for self-test through retail pharmacies, online sales platforms and other channels. Antigen detection is also applicable to: people who go to grass-roots medical and health institutions with respiratory tract, fever and other symptoms within 5 days; Isolation and observation personnel, including personnel in home isolation and observation, close connection and secondary close connection, entry isolation and observation, sealing and control area and control area. At present, there are many asymptomatic infections in the epidemic. Can they be screened by antigen detection? Li Jinming believes that from the existing data, most of the infected people of Omicron variant are asymptomatic, but it does not mean that their viral load is low. On the contrary, some studies have shown that the viral load in the pharynx of some asymptomatic infected people is quite high. "If it is an infected person among the isolated observers, there is a high probability that the antigen can be detected once a day." Li Jinming said that even if the antigen test is positive, it still needs to be confirmed by nucleic acid test. How does antigen self-test positive do? Timely report to the community Novel coronavirus pneumonia, Li Jinming said, according to the plan, the positive self testing personnel of the antigen should report to the community (village or town) immediately, whether it has respiratory or fever symptoms. The community (Village) contact emergency center will transfer the residents to the medical institutions with fever clinic and carry out nucleic acid detection according to the new guidelines for the transport work of the new crown pneumonia related personnel. At the same time, the sampling swabs, sampling tubes and test cards used by positive personnel are put into sealed bags and transferred to medical institutions for medical waste disposal. For those who have negative antigen self-test but have symptoms, according to the scheme, it is recommended to go to the medical institution with fever clinic as soon as possible for nucleic acid detection. "If it is inconvenient to see a doctor, you should isolate yourself at home, avoid going out for activities, and conduct antigen self-test once a day for five consecutive days." Li Jinming said. (outlook new era)
Edit：Yuanqi Tang Responsible editor：Xiao Yu
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