On June 9, the Joint Prevention and Control Mechanism of the State Council held a press conference to introduce the situation of nucleic acid testing and epidemic prevention and control. At the meeting, a reporter asked about the reasons for false positives and false negatives in nucleic acid tests. Some reporters also asked about patients who had multiple negative nucleic acid tests, but finally came back positive. In this regard, Li Jinming, deputy director of the National Health Commission’s Clinical Laboratory Center, made an authoritative response.
Li Jinming, deputy director of the National Health Commission’s Clinical Laboratory Center
Li Jinming said that there should be three problems with false negatives. One is the sampling time. For example, a patient is infected very early, and the concentration of the virus attached to his throat does not reach the detection limit of the detection method, so it cannot be done. Another is that the infection time is too long, such as more than 10 days or half a month. If it exceeds this long, he will be in a state of recovery, antibodies will be produced, and the possibility of positive detection will be greatly reduced.
The second is quality control. The first is sampling. The sampling operation is not in place, no qualified samples are collected, and where to put the samples after they are collected, including where they are placed before transportation. If it is not stored at low temperature, it will be unstable in summer. After the samples arrive in the laboratory, whether there is strict quality control in the laboratory’s testing, whether the reagents and instruments are matched, including whether there are strict procedures for human operation, these are also factors that cause false negatives.
The third is data falsification and violation of laws and regulations. The third-party laboratory falsely reported its own testing capabilities and collected samples beyond its own capabilities. The samples could not be tested within the specified time, so they conducted data fraud and falsely reported the results. In such a situation, it is a violation of laws and regulations, and some laboratories reduce the amount of testing by remixing the samples, resulting in distorted results.
About false positives, Li Jinming said there are two reasons. One is the legacy contamination of amplification products. Nowadays, large-scale population screening requires a lot of work, and people do not stop without stopping. That is to say, between each batch, there may not be so much time to do some cleaning in the laboratory. Coupled with the tightness of the reaction tube, Not all of them are well sealed. If a positive sample or quality control sample happens to be encountered, it will leak if there is a problem with its sealing, which will cause laboratory contamination, and false positives such as related weak positives may occur. Positive result.
Secondly, cross-contamination occurs between samples during the detection process, such as positive samples or positive quality controls contaminating originally negative samples. Some laboratories are doing suspicious positive samples, and they will be reported as positive in the initial test. This nucleic acid test report has a relatively high risk, because it may be found to be false positive after review.
Li Jinming emphasized that some of the problems mentioned above are difficult to avoid, and they exist objectively. Some are quality management and quality control issues that require continuous improvement. There are still some issues involving illegal and criminal activities, and drastic measures should be taken to crack down on them.
As for the case where the nucleic acid test is negative for many times in a row, and finally positive, Li Jinming said that most people will not have this situation, but it has happened. There are three reasons for this. One is that the person was not infected at the beginning, but was infected at a later point in time, and tested positive after infection. The second is that it is in the incubation period and has not been detected, and the test is positive after the onset of the disease. The third is that although the virus was present at the beginning, the load did not reach the lower limit of detection, and it was not detected, but after the load was high, it was tested positive.
Red Star News reporter Hu Yiwen Wu Yang reported in Beijing
Editor Guan Li
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