Recently, important changes have taken place in the epidemic trend and prevention and control measures. On March 10, the application plan for antigen detection of the new crown virus was officially released. Ordinary people also have questions, what is the difference between antigen detection and nucleic acid detection? Which method is more accurate? Will self-testing be the mainstay in the future? What do I need to pay attention to when testing at home? What can be done to improve accuracy? What precautions should be taken in the face of test results? Let's explain the main points for you now.
First of all, we need to understand that different detection methods have different accuracy rates, so the scope and timing of application are not the same. To measure the accuracy of the detection method, it is usually necessary to look at 2 important indicators, false negative and false positive. False negative refers to infection, but because the sensitivity of the detection method is not enough, the result is negative, in short, a certain proportion of infection, not reflected in time. False positives refer to cases where specificity is not enough, and those who are not infected are also shown positive.
Nucleic acid detection, for nucleic acid fragments, the sensitivity is high, the main method currently used is real-time fluorescence quantitative PCR, the sensitivity is 10 per milliliter of 3 power copies. An indicator that measures different sensitivities is called Ct value, which indicates the amplification multiple of nucleic acids, and the specific operation method is to ensure that when the sample contains fewer nucleic acids, it can also be detected. Test results can also be positive with low Ct values, indicating a high viral load. Casually say 1 sentence, if you do not mention the Ct value, only say that the nucleic acid result is positive, in fact, there is not much clinical significance. In addition, the Ct value is too high, for example, when it reaches 40, the measured positive result is beyond the scope of medical diagnosis, and the positive nucleic acid does not represent infectiousness, for example, the positive result obtained by the environmental sample in the case of a high Ct value can only indicate that the environmental sample may have been contaminated with the virus, but the positive is not evidence of the presence of a live virus or infection in the sample.
The accuracy of nucleic acid detection and antigen detection is affected by a variety of factors. The current detection method, when the Ct value is less than 25, the consistency between nucleic acid detection and antigen detection is about 95.8%, when the Ct value is higher than 25, the consistency is about 50.7%, and when the Ct value is higher than 30, the consistency is only 20.9%. Thus, the proportion of false negatives on antigen test results is higher, but infected people with a higher viral load or more contagiousness can be found. Studies have shown that in the process of infection with the new crown virus in vitro, the virus replication will reach a peak within 24 hours, which is speculated that after the human body is infected with the new crown virus, it will reach the lower limit of antigen detection in 24 to 48 hours, if the antigen test result is negative, and the nucleic acid test is positive, it may be that the Ct value is greater than 30, indicating that the viral load has decreased and the infectivity has been greatly reduced.
Regarding the effectiveness of antigen detection, many drills have been carried out since last year, and the accuracy rate has been tested. For example, a total of 16,000 antigen rapid detection reagents were distributed in a certain place, 15,022 valid data were collected, the detection completion rate within 8 hours was 75.11%, and 15,017 people were judged to have negative results by the intelligent identification system, and the consistency with professional review was 99.97%. Studies have shown that antigen testing, although less sensitive, that is, has been infected, but after 1 test, may not show a positive result. As a result, patients in the incubation or post-infective phase cannot be detected in time, but the sensitivity of antigen testing can cover the entire infectious period, and the vast majority of infectious cases can be detected by testing at least 3 times a week. Therefore, extensive active antigen testing can detect infected people with mild or asymptomatic symptoms, and these people, timely isolation measures, can help reduce the spread of the virus in families and communities.
According to the requirements of the application plan, the applicable population of antigen detection mainly includes 3 kinds, 1, to the primary health institutions for treatment, accompanied by respiratory tract, fever and other symptoms, and symptoms appear within 5 days of the person. 2. Home isolation, close and sub-close connection, entry isolation observation, sealing and control area and control area of isolation and observation personnel. Third, residents of communities with antigen self-testing needs. The overall strategy is to face the public, on the basis of nucleic acid detection, to add antigen detection as a supplement. Antigen testing is a complementary tool for screening specific populations to help improve the ability to detect early. Therefore, ordinary people should remember that they can perform antigen testing as needed, but they cannot replace nucleic acid testing, that is, if they receive a notification, for example, the health code changes color, or receive a text message requesting testing, they should actively cooperate and cannot refuse nucleic acid testing requirements because they have done antigen testing.
Antigen testing, for applicable objects over the age of 14, can be self-tested, home testing, need to operate in accordance with the regulations, in order to ensure accuracy. The specific method is to wash your hands first, and use a tissue to blow off the nose, and then, unpackaged the nasal swab and avoid touching the head of the swab with your hands. Subsequently, the head is slightly tilted, 1 hand holds the swab of the tail, enters against the nostril on the side, along the bottom of the lower nasal passage, 1 to 1.5 cm deep backwards, and rotates at least 4 times against the nasal cavity. When completed, use the same swab again and perform the same operation on the other side of the nasal cavity. Children between the ages of 2 and 14, with the help of others to take samples. After sample collection, place the nasal swab in the sampling tube, swirl and mix well in the stock solution for 30 sec, and squeeze the swab head at least 5 times to ensure that the sample is adequately eluted. Then, drop the liquid into the test card and wait for the result. Finally, swabs and test cards need to be processed as required and test results recorded or reported. Antigen detection kit, the price is cheap, after learning the theory, you can buy your own kit, at home for 1 test exercise.
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