The nucleic acid test was positive, but why was the antigen negative when I made it at home? The doctor tells the reason behind
With the development of the epidemic situation, frequent "nucleic acid for all employees" has been canceled in many places. At the same time, there is a large gap for medical workers and fewer nucleic acid testing points. Simple nucleic acid testing can no longer meet the needs of the people. For the COVID-19 virus The screening method of nucleic acid and antigen is mostly used alternately.
Many people have questioned the accuracy of the two. What are the principles of the two detection methods? Which is more accurate? Some people tested negative for antigen but positive for nucleic acid. What is going on?
What are the principles of the two detection methods? Which is more accurate?
COVID-19 pneumonia nucleic acid detection is to find out whether there is nucleic acid of foreign invading virus in respiratory specimens, blood or feces of patients, and determine positive patients through real-time fluorescent RT-PCR detection.
The new coronavirus is a virus containing only specific RNA. If the specific nucleic acid sequence of COVID-19 virus is detected in the patient's sample in the laboratory, it indicates that the patient may be infected by the new coronavirus. If there is no Ct value or the Ct value is greater than 40, it is judged as negative. If the Ct value is less than 37, it can be reported as positive. If the Ct value is between 37-40, it is recommended to repeat the test. Antigen detection is to detect whether the nasal/pharyngeal swab contains the protein of the COVID-19 virus. It is composed of the internal genetic material RNA and the external protein shell. The protein is the "coat" of the virus and determines the specificity of the virus antigen. .
Nucleic acid detection uses PCR technology to perform RNA amplification to complete the detection. It has high sensitivity and is the gold standard for judging the diagnosis of COVID-19. Antigen detection is the N protein with the largest number of virus particles. The detection result has a false negative probability and cannot be completely Instead of nucleic acid detection, antigen detection is only an auxiliary detection and cannot be used as the basis for the diagnosis of COVID-19 pneumonia infection.
Antigen test is negative, but nucleic acid test is positive, what is going on?
COVID-19 antigen detection has a probability of 75%-98% to detect positive cases, and a probability of 95%-99% to exclude negative cases. At present, the sensitivity of the antigen kits approved for marketing in China is between 75% and 98%. Generally speaking, the detection rate is quite high, but because it may have false positives and false negatives, it cannot completely replace nucleic acid detection. The specific probability There is no exact numerical data displayed yet.
If the self-test antigen at home is positive, then there is a high probability that it is positive. You must take good precautions and avoid contact with others as much as possible.
epilogue
The author here reminds everyone that antigen detection and nucleic acid detection have their own advantages and disadvantages and complement each other. Nucleic acid detection takes a long time and results are slow, but the sensitivity and accuracy are high; antigen detection is easy to operate and the results are fast, people can test themselves at home, and at the same time avoid cross-infection. It is worth mentioning that nucleic acid fraud incidents frequently occurred in some local testing institutions, and they were banned repeatedly, causing very bad effects, seriously interfering with people's lives and epidemic prevention and control work, and causing huge losses to the country and the people. The reason for nucleic acid fraud is mainly due to huge profits and low crime costs.