Cover reporter Shao Meng
On June 9, the Joint Prevention and Control Mechanism of the State Council held a press conference to introduce the work of nucleic acid testing and epidemic prevention and control.
At the meeting, a reporter asked whether rapid and mixed tests are widely used. Will this reduce the accuracy of nucleic acid tests? What are the reasons for false positives and false negatives in nucleic acid tests? Is it possible to avoid it?
Li Jinming, deputy director of the National Health Commission’s Clinical Testing Center, said that the reagents for rapid testing can be divided into two categories. One is low-throughput, that is, each test can detect 1-16 samples. It is mainly used for fever clinics and emergency patients, and the time required is 30-50 minutes. There is another type that can be used for population screening. It can detect more than 90 samples at a time, and the amplification time is about 30 minutes faster than usual, which speeds up the detection speed. As long as it is done strictly according to the specifications, there is no problem with the rapid inspection.
Li Jinming, deputy director of the National Health Commission’s Clinical Laboratory Center. Source: China Network
About mixed detection, after theoretical verification, laboratory verification, and on-site verification of real patient samples from the outbreak, its mixed detection rate There is no obvious gap with the single sample book, and the detection is accurate and reliable.
Li Jinming said that false negatives should have three problems:
First, 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 detected. If the infection time is too long, such as more than 10 days or half a month, the patient is in a state of recovery and antibodies are produced, and the possibility of positive detection is greatly reduced.
The second is quality control. The sampling operation is not in place, the qualified samples are not collected, and where the samples are placed after sampling, where they are placed before transportation, etc. will all affect. If it is not stored at low temperature, it will be unstable in summer. After the sample arrives in the laboratory, whether the laboratory has strict quality control for testing, whether the reagents and instruments are matched or not, including whether there is a strict process for human operation, are all factors that cause false negatives.
The third is data falsification and violation of laws and regulations. Many third-party laboratories falsely report their testing capabilities and collect samples beyond their own testing capabilities. The samples cannot be tested within the specified time, and the data is falsified and the results are falsely reported. Other laboratories reduce the amount of testing by remixing the samples, resulting in distorted results.
Li Jinming pointed out that there are two main reasons for the occurrence of false positives:
First, the contamination of amplification products. Nowadays, large-scale population screening requires a lot of work, and people do not stop without stopping. Between each batch, there may not be so much time to do some cleaning in the laboratory. In addition, not every reaction tube is well sealed. , If you happen to encounter a positive sample or quality control sample, leakage will occur if there is a problem with sealing, which will cause laboratory contamination, and false positive results such as related weak positives may occur.
Secondly, cross-contamination occurs between samples during the detection process, such as positive samples or positive quality controls contaminating originally negative samples. Some labs are doing suspicious positive samples, and they will report them as initial positives, which has a greater risk, because it may be found to be false positives after review.
Li Jinming emphasized that some of the above problems are difficult to avoid, and their existence has objectivity. 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.
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