Experts suggest that the combined use of multiple respiratory-tract samples of the patients in testing improve the positive test rate. Therefore, Diagnosis and treatment of COVID-19 (fifth edition) has changed the oropharyngeal swabs to nasopharyngeal swabs ( 13). In practice, the positive rate of nucleic acid test using nasopharyngeal swabs is higher than that using oropharyngeal swabs ( 11, 12). Nasopharyngeal swabs should be acquired by scraping in the deep nasal cavity repeatedly ( 10). In addition, patients are too sensitive and become uncooperative during sampling. Some medical personnel, who lack experience and have greater mental stress than usual, fail to collect the samples in the right place with the optimal way, and are unable to obtain perfect epithelial cells. Swabs should be scraped from deep down the isthmus faucium around the uvula and palatine tonsils repeatedly ( 7- 9). ![]() Sampling of oropharyngeal swabs demands expertly operators. On the other hand, reason for the low positive rate of nucleic acid test in upper-respiratory-tract samples is largely due to unqualified samples. Due to the specific clinical conditions as well as patient intolerance (for example, the sputum sample should be obtained by deep coughing after washing oral cavity, while many severely ill patients become very weak and fail to provide qualified samples but mostly saliva), nasopharyngeal and oropharyngeal swabs are the mainly used samples for nucleic acid test. However, collection of lower-respiratory-tract samples is very difficult. It was reported in some cases that nucleic acid test results of swabs were negative before hospitalization, whereas diagnosis were eventually confirmed by using bronchoalveolar lavage fluid in a few cases ( 6). According to experience from SARS, viral loads and genome fractions in lower-respiratory-tract samples are high ( 5), so lower-respiratory-tract samples should be used for testing, followed by nasopharyngeal and/or oropharyngeal swabs. Upper-respiratory-tract samples include nasopharyngeal and/or oropharyngeal swabs and aspirates, and lower-respiratory-tract samples include phlegm, respiratory aspirates, bronchoalveolar lavage fluid, and lung biopsy samples. Respiratory tract samples are often used. Quality of microbial samples affect results strongly. Possible causes of false-negative results Pretest processes Sample collection In this study, we analyzed the causes of false-negative results in nucleic acid test in COVID-19 from the perspective of clinical laboratory and explored measures accordingly. Researchers believe that the positive rate of nucleic acid test of SARS-CoV-2 is approximately 30–50% ( 2- 4). However, with an increasing number of false-negative results of nucleic acid test and the serious consequences therefore ( 1), first-line clinicians are starting to believe that nucleic acid test is not reliable, and they have been recommended to use imaging results as a more accurate auxiliary diagnostic tool ( 1). To respond to the needs of outbreak prevention, rapid diagnosis, and disease monitoring, companies and clinical laboratories have quickly developed nucleic acid test kits for SARS-CoV-2 and put them into clinical application. Guidelines issued by the National Health Commission of the People’s Republic of China proposed that one of the diagnostic criteria be positive result of nucleic acid test of SARS-CoV-2 in respiratory or blood samples of patients ( 1). At the same time, the International Committee on Taxonomy of Viruses named this pathogen severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). On February 11, 2020, the World Health Organization (WHO) named the novel coronavirus-induced pneumonia as coronavirus disease 2019 (COVID-19). Until February 14, 2020, China had 66,383 confirmed cases already. ![]() Since December 2019, there had been an outbreak of a novel coronavirus-induced pneumonia across the world. ![]() Keywords: Coronavirus disease 2019 (COVID-19) real-time fluorescence polymerase chain reaction (RT-PCR) nucleic acid test
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