To study the difference in the extraction efficiency of the novel coronavirus (2019-nCoV) nucleic acid by using magnetic beads method, centrifugal column method and one-step method.

On March 5, 2021, 10 throat swabs were collected from the staff working in the nucleic acid sampling room in Department of Clinical Laboratory, Affiliated Taikang Xianlin Drum Tower Hospital, Medical School of Nanjing University. The positive quality control samples were mixed into the swabs and used as mock positive samples. The RNA was extracted from simulated positive samples and their diluted samples by using magnetic beads method, centrifugation column method and one-step method. The purity (A₂₆₀/A₂₈₀ ratio) and concentration of the nucleic acid obtained were measured by micro-uv photometry, and fluorescence quantitative PCR was performed to compare the CT value and extraction efficiency. The three methods were used to extract the simulated weak positive specimens and to compare the difference of CT values after amplification. The measurement data that followed normal distribution were expressed by x¯±s, the t test was used for comparing in the same group, and single factor analysis of variance was used for comparing among multiple groups. A P value smaller than 0.05 indicated a significant difference.

2019-nCoV nucleic acid extracted by magnetic bead method, centrifugal column method and one-step method could amplify positive results. There was no significant difference between the CT value of RNA amplification extracted by magnetic bead method and one-step method (t=‒ 0.995, P=0.376). The CT values of orf1ab gene amplified by centrifugal column method, magnetic bead method and one-step method were 29.28±0.06, 30.82±0.14 and 29.79±0.01 respectively (F=11.196, P=0.041). The CT values of E gene were 28.52±0.40, 27.33±0.78 and 27.38±0.13 respectively (F=3.407, P=0.169). The CT values of N gene were 28.61±1.02, 27.24±0.20 and 27.25±0.47, respectively (F=2.880, P=0.020). The CT values of human genes extracted by centrifugal column method, magnetic bead method and one-step method were 19.68±0.36, 20.14±0.06 and 20.58±0.49 respectively, which was statistically significant (F=4.904, P=0.048). The CT value of amplified human gene was affected by the dilution of human samples twice. The CT value of undiluted samples was smaller than that of diluted samples twice, with a difference of 2.95±0.22, which was statistically significant (t=‒3.025, P=0.039). The extraction time of one-step method, magnetic bead method and centrifugal column method were (15.00±1.50), (20.00±1.50) and (40.00±5.5) min respectively, and the difference was statistically significant (F=688, P=0.027).

Magnetic bead method, centrifugal column method and one-step method can be used to extract 2019-nCoV nucleic acid, for the centrifugal column method has a higher extraction efficiency than the magnetic bead method and the one-step method. The one-step method is the fastest, followed by the magnetic bead method and the centrifugal column method. A large number of clinical samples can be processed using the magnetic bead method and one-step method. One-step rapid nucleic acid test can also be performed on samples from emergency and fever clinics. It is not recommended to dilute specimens for testing. In order to improve the detection rate, extracting RNA from highly suspected samples with negative initial nucleic acid test by centrifugal column method is suggested.

2019-nCoV; Nucleic acids; Clinical laboratory techniques