(People’s Daily Health Client Reporter Yin Wei) As an important supplement to the epidemic prevention work, antigen testing has the advantages of not requiring professionals, venues and instruments, and quick results, so it has been widely used in this round of epidemics. What should I do if I test positive for the new crown antigen at home? Is the difference between the results of the new crown antigen test and nucleic acid test a quality issue? A reporter from the People’s Daily Health Client interviewed Song Haibo, President of the Medical Inspection Industry Branch of the National Health Industry Enterprise Management Association and Vice President of the Shanghai Research Institute of Experimental Medicine, and asked him to give an authoritative interpretation.
The home antigen test is positive, what should I do?
Song Haibo said, don’t be nervous if two bars are found in the antigen test at home. If you have been isolating at home and have no symptoms, you may wish to do another antigen before reporting. retest. However, when retesting, it is recommended to change a batch number or retest a product from another manufacturer. “If it is still positive, the positive indication may be greater, and it needs to be reported as soon as possible, waiting for the nucleic acid test to confirm. If the nucleic acid test is negative, it means that the antigen test has encountered a problem. False positives have arrived.”
He reminded that there are multiple reasons for the false positives of the new crown antigen test. First of all, the composition of human nasopharyngeal specimens is complex, and it will be interfered by endogenous and exogenous substances. When there are other microbial infections, or when you have been vaccinated, taken certain drugs or special foods, the samples may exist. Interfering substances, leading to false positive results.
He emphasized that Sampling of corresponding samples in strict accordance with the reagent instructions is the premise for the authenticity of the test results. Because the antigen detection kits test objects are human samples, such as nasal swabs, nasopharyngeal swabs, not the popular online samples of orange juice, cola, vinegar, including fish. “If the test is not carried out according to the instructions, the false positive result cannot be attributed to the quality of the reagent.”
The components of different antigen test products are different and cannot be mixed. p>
In addition, if the background of the detection card is blurred, there is no detection line, or there are abnormal conditions such as water spots, spots, blanks, etc., it may be that the lysis solution was added too quickly or too much, or the lysis solution was mistakenly dropped into the The detection window causes. Generally, the test results are usually read as correct results within 15 minutes to 30 minutes. If the time is too long, false results will appear, which cannot be used as the basis for interpretation and should be re-tested.
In addition, there may be several brands of antigen reagents distributed at home at the same time. Song Haibo believes that if reagents, extracts, sampling swabs, and ordinary cotton swabs from different manufacturers are used instead of matching swabs, these may lead to false positives. This is because the specific extracts and sampling swabs of different manufacturers look similar, but the components are different, so they cannot be mixed.
The detection principle of the novel coronavirus antigen reagent is the specific binding reaction of antigen and antibody. Song Haibo explained that the specific binding of antibodies to the new crown antigen to be tested is colloquially like a key and a lock. In theory, a lock can only be opened by a specially matched key, and other keys cannot open the lock. Theoretically, only when the target substance antigen to be detected exists in the sample can it specifically bind to the antibody coated in the detection reagent, resulting in color development at the T line position.
Why is there still a gap between the specificity and sensitivity of COVID-19 antigen detection and nucleic acid? Song Haibo said that this is because the new crown antigen, like all immuno-methodological detection reagents, has a certain probability of false positives or false negatives. For example, one key can open several locks or one lock can be opened by several keys. And non-specific problems are an unavoidable common phenomenon in all immune tests. Therefore, false positives or false negatives in the new crown antigen test are objectively unavoidable.