Nucleic acid testing process for new coronaviruses
For nucleic acid testing of novel coronaviruses, samples are first collected according to the [sample requirements] section of the kit instructions. The conventional sample types include pharyngeal swabs, nasal swabs, sputum, bronchial lavage fluid, alveolar lavage fluid, etc.
Since the novel coronavirus is an RNA virus and RNA is easily degraded, RNA-free swabs and RNA-free storage tubes are used for sample collection. After obtaining the patient samples, they need to be tested as soon as possible. If the samples that need to be transferred cannot be tested immediately, they should be cryo-encapsulated according to the instructions and sent to a specialized testing institution for testing.
Upon receipt of the sample, the testing facility will perform nucleic acid extraction. The nucleic acid extraction reagent should be the nucleic acid extraction kit specified in the approved product specification.
The viral RNA needs to be reverse transcribed to cDNA first and then amplified for testing. PCR amplification and testing should be performed using the fluorescent quantitative PCR instrument specified in the approved product specification, and the size of the Ct value of the sample obtained by the fluorescent quantitative PCR can determine whether the patient sample contains the novel coronavirus.
Factors affecting the accuracy of nucleic acid testing
The accuracy of nucleic acid test results is not only related to the accuracy of the test kit itself, but also closely related to the timing of the test sample collection and the type of test sample. First of all, the timing of sampling is important. If the patient has just eaten or brushed his teeth, and the virus in the pharynx has been washed away, it is easy for the nucleic acid test to show negative results even in patients who are positive for viral infection.
Therefore, experienced health care professionals usually ask patients not to drink or eat before collecting respiratory samples.
Test results are also related to the type of sample to be tested. Test results can vary greatly between different samples collected from the same patient at the same time. I have been directly involved in testing thousands of clinical samples since the onset of the outbreak, and among the samples tested so far in patients with novel coronavirus infections, the amount of viral nucleic acid in lung lavage and sputum is usually higher than in respiratory swabs such as nasal and pharyngeal swabs, and the amount of viral nucleic acid in respiratory swabs is much higher than in blood. In addition, the amount of virus in the patient's body changes dynamically as the course of the disease continues to change. Therefore, it is true that the results of sampling and testing may vary from time to time.
Currently, the new coronavirus nucleic acid test uses a fluorescent PCR method that takes only 30 minutes to produce a result.
The fastest is currently the one that gives results in 3-15 minutes.
