Practice and exploration of novel coronavirus nucleic acid detection in designated hospitals

Abstract

Objective: To explore the related problems and solutions in nucleic acid detection of COVID-19 patients at the present stage, and to provide reference for clinical laboratories. Methods: A total of 462 patients admitted from April 1 to April 10 were selected and their basic Ct values and time changes were analyzed. The false-negative test results caused by sample collection from March 20 to March 31 and from April 1 to April 10 were statistically analyzed, respectively. A total of 213 clinical samples were selected for parallel detection using reagents A and B to compare the differences between them. According to relevant documents, make the reinspection standard operation procedure (SOP) document of suspicious samples. According to the quality control method of quantitative test, weak-positive control was prepared and tested 5 batches every day for 4 days, and 20 groups of data were obtained and used as the initial data to make quality control charts. Results: The median Ct values of ORF1ab and N gene in 462 patients were 24.50 (20.58-32.10) and 23.38 (19.43-31.24), respectively. In 184 patients with Ct value less than 30, the median time for Ct value to rise above 30 was 6 days (4-8 days). The sampling unqualified rates were 12.4% and 2.4% in the early and late stages, respectively, and the difference was statistically significant (P<0.01). The consistency of the two reagents was good in the detection of samples with Ct values less than 30, but decreased in the detection of samples with Ct values between 30 and 40. The Ct values of ORF1ab and N gene in weak-positive control were 35.17±0.55 and 35.23±0.88, respectively, which can better monitor the detection of clinically concerned samples with Ct values within the range of 35. Conclusions: For COVID-19 patients with basic Ct value less than 30, the frequency of nucleic acid test can be set to once every 3 or 4 days. The difference between the two regents in detection of the smple with Ct value less than 30 is minor, but for the sample with Ct value 30-40, the difference is apparently large. Laboratories should establish the standards and procedures for sample re-test, and the quality monitoring at the level of Ct value 35 should be strengthened to ensure the consistency of COVID-19 nucleic acid test results.

Keywords

• |covid-19|sars-cov-2 nucleic acid detection|cyclic threshold|quality control