Improving the preanalytical stage of COVID-19 laboratory diagnosis: evaluation of biomaterials and innovative swab materials

The global COVID-19 pandemic has necessitated mass population testing, highlighting the critical importance of the preanalytical stage of diagnostics. This study aimed to comparatively evaluate the effectiveness of using saliva as an alternative biomaterial and nasopharyngeal swabs collected using flocked and traditional cotton swabs for PCR diagnosis of SARS-CoV-2. A prospective study was conducted on 31 patients with parallel collection of saliva and nasopharyngeal swabs. It was shown that the mean threshold cycle (Ct) value for detecting the human genome in saliva was 3 points higher, and the viral load was significantly lower, indicating lower sensitivity of PCR analysis of saliva (mean Ct deviation for SARS-CoV-2 — -3,175). The second part of the study involved a paired comparison (n=217) of the collection efficiency of flocked and cotton swabs. Statistical analysis (paired t-test, t(24)=5.856; p<0.00001) revealed a highly significant advantage of flocked swabs: the mean difference in efficiency was ΔM = 3,74 ± 3,19 units, 0.00001) revealed a highly significant advantage of flocked swabs: the mean difference in efficiency was ΔM = 3,74 ± 3,19 units, Cohen's d effect size=1,171. The results demonstrate the critical importance of the choice of biomaterial and collection tools at the preanalytical stage. Nasopharyngeal swabs collected with flocked swabs are the preferred method for achieving maximum sensitivity in PCR diagnosis of SARS-CoV-2, while saliva can be considered an acceptable alternative only in exceptional cases.

1. WHO. (2020). Laboratory testing for coronavirus disease 2019 (COVID-19) in suspected human cases. – URL: https://www.who.int/publications/i/item/10665-331501 (дата обращения: 20.05.2025).

2. Diagnostic accuracy of serological tests for COVID-19: systematic review and meta-analysis / B.M. Lisboa, G. Tavaziva, S.K. Abidi [et al.] // BMJ. – 2020. – Vol. 1. – P. 370:m2516. doi: 10.1136/bmj.m2516.

3. Saliva or Nasopharyngeal Swab Specimens for Detection of SARS-CoV-2 / A.L. Wyllie, J. Fournier, A. Casanovas-Massana [et al.] // N. Engl. J. Med. – 2020. – Vol. 383(13). – P. 1283-1286. doi: 10.1056/NEJMc2016359.

4. Saliva sample as a non-invasive specimen for the diagnosis of coronavirus disease 2019: a cross-sectional study / E. Pasomsub, S.P. Watcharananan, K. Boonyawat // Clin. Microbiol. Infect. – 2021. – Vol. 27(2). – e1-285.e4. doi: 10.1016/j.cmi.2020.05.001.

5. Evaluation of Specimen Types and Saliva Stabilization Solutions for SARS-CoV-2 Testing / S.B. Griesemer, G. Van Slyke, D. Ehrbar [et al.] // J. Clin. Microbiol. – 2021. – Vol. 59(5) – P. e01418-20. doi: 10.1128/JCM.01418-20.

6. Saliva is less sensitive than nasopharyngeal swabs for COVID-19 detection in the community setting / D. Becker, E. Sandoval, A. Amin [et al.] // medRxiv. – 2021. doi:https://doi.org/10.1101/2020.05.11.20092338.

7. Infectious Diseases Society of America Guidelines on the Diagnosis of COVID-19:Serologic Testing / K.E. Hanson, A.M. Caliendo, C.A. Arias [et al.] // Clin Infect Dis. – 2020. – ciaa1343. doi: 10.1093/cid/ciaa1343.