What are the current sensitivities and specificities of the standard and rapid COVID-19 tests, and is there a difference in testing symptomatic patients or in low prevalence situations? 

Posted on May 16, 2020 by Brie Cawston-Grant

Summary

Clinical testing characteristics of SARS-CoV-2 rapid testing devices authorized in Canada are very limited. Analytical testing characteristics are available from individual manufacturers of the 19 authorized devices. For standard testing performed in Canada, false negative rates based on prevalence are available in Table 1 from the Alberta Health Services (AHS) COVID-19 Scientific Advisory Group (1).

I.   Background information in testing:

  • Real time, reverse transcriptase polymerase chain reaction (RT-PCR), is a type of nucleic acid amplification test. This is currently the “standard” or validated testing used in Canada.
  • Current anatomical collection sites are either nasopharyngeal (NP), nasal, or throat swabs. Sensitivity of testing is largely determined by sample collection technique. Nasal swabs were found to have inferior sensitivity compared to NP and throat swabs in preliminary data of a small Alberta based study (1). Further information on factors that determine sensitivity can be found in the following REAKT question:

 

“What factors affect sensitivity and specificity of the COVID-19 nasal swab?”

 

  • A list of diagnostic devices for COVID-19 submitted for approval by health Canada are available (2). As of writing, there are 31 devices submitted.
  • A list of testing devices authorized by Health Canada is available (3). As of writing there are two point-of-care devices that have been authorized: The Spartan Cube COVID-19 System from Spartan Bioscience Inc (research use only), and the Xpert Xpress SARS-CoV-2 from Cepheid. Note that the Spartan Cube was recently recalled from clinical use (4, 5). 
  • Health Canada authorized devices that utilize serological testing are the Liaison Sars-CoV-2 S1/S2 IgG from Diasorin Inc., and SARS-CoV-2 IgG Assay from Abbott Laboratories (3).

II.   Sensitivity and specificity of standard testing (RT-PCR only):

  • linical sensitivity and specificity values have not been determined for lab developed RT-PCR testing in Canada (1).
  • Analytical specificity of PCR testing is 100% when done during the active infection phase.
  • Analytical sensitivity of RT-PCR is high with a 95% limit of detection (LOD).
  • Clinical sensitivities for RT-PCR testing with NP swab collection have been found to be 71-95% by non-Canadian countries (6-8).
  • Table 1 from AHS COVID-19 Scientific Advisory Group report gives false negative rates according to pretest probabilities for 90% and 80% sensitive RT-PCR tests (1). If the likelihood of disease is high, the likelihood that a test may be falsely negative is increased.

III.   Sensitivities and specificities of commercially available devices:

  • Clinical sensitivities and specificities of commercially available rapid testing devices are very limited. Analytical sensitivities and specificities are available from individual manufacturers.
  • The majority of tests available are nucleic acid test (NAT) based technologies.
  • As an example, analytical sensitivity of the NAT based Xpert ® Xpress SARS-CoV-2 from Cepheid is greater than 95%, and there wasn’t cross reactivity detected against non SARS-CoV-2 samples (9).
  • Analytical sensitivity and specificity of the serological based Liaison ® SARS-CoV-2 S1/S2 IgG from Diasorin Inc. are 90.4% for 5-15 days from disease onset and 98.9%, respectively (10).

Questions? Comments? Does this need to be updated? Do you have valuable points to add ? Please email ask.reakt@ubc.ca.

References

  1. Alberta Health Services COVID-19 Scientific Advisory Group. How do the testing characteristics for the Alberta Health Services lab-developed test for COVID-19 differ between samples collected from nasal, nasopharyngeal, and throat swabs? 15 April 2020 [Internet].  https://www.albertahealthservices.ca/assets/info/ppih/if-ppih-covid-19-sag-comparison-of-testing-sites-rapid-review.pdf (accessed 16 May 2020).
  2. Health Canada. Diagnostic devices for use against coronavirus (COVID-19): list of applications received. 15 May 2020 [Internet] https://www.canada.ca/en/health-canada/services/drugs-health-products/medical-devices/covid-19/diagnostic-devices-applications.html (accessed 16 May 2020).
  3. Health Canada. Testing devices for the use against coronavirus (COVID-19): list of authorized devices. 15 May 2020 [Internet] https://www.canada.ca/en/health-canada/services/drugs-health-products/medical-devices/covid-19/diagnostic-devices-authorized.html (accessed 16 May 2020).
  4. Bench A. Recall issues for rapid coronavirus test with $9.5M Alberta Health Services contract. Global News. 3 May 2020 [Internet]. https://globalnews.ca/news/6899733/spartan-covid-19-recall-ahs-testing/ (accessed 16 May 2020).
  5. Simonjic P, Kapelos V. Rapid COVID-19 test restricted by Health Canada will be fixed by summer, company’s CEO says. CBC News. 4 May 2020 [Internet]. https://www.cbc.ca/news/politics/spartan-bioscience-testing-device-back-out-summer-1.5555226 6 May 2020.
  6. Xie X, Zhong Z, Zhao W, Zheng C, Wang F, Liu J. Chest CT for Typical 2019-nCoV Pneumonia: Relationship to Negative RT-PCR Testing. Radiology [Internet]. 12 Feb 2020 [cited 16 May 2020]. Available from: https://pubs.rsna.org/doi/10.1148/radiol.2020200343 [Epub ahead of print].
  7. Fang Y, Zhang H, Xie J, Lin M, Ying L, Pang P et al. Sensitivity of Chest CT for COVID-19: Comparison to RT-PCR. Radiology [Internet]. 19 Feb 2020 [cited 16 May 2020]. Available from: https://pubs.rsna.org/doi/10.1148/radiol.2020200432 [Epub ahead of print].
  8. Luo L, Liu D, Liao X, Wu X, Jing Q, Zheng J et al. Modes of Contact and Risk of Transmission in COVID-19: A Prospective Cohort Study 4950 Close Contact Persons in Guangzhou of China. SSRN Electronic Journal [Internet]. 26 March 2020 [cited 16 May 2020). Available from: https://www.medrxiv.org/content/10.1101/2020.03.24.20042606v1 [Epub ahead of print].
  9. Cepheid. Xpert ® Xpress SARS-CoV-2. Apr 2020 [Internet] https://www.fda.gov/media/136314/download (accessed 16 May 2020).
  10. Liaison Inc. Liaison SARS-CoV-2 S1/S2 IgG. Apr 2020 [Internet]. https://www.diasorin.com/sites/default/files/allegati/liaisonr_sars-cov-2_s1s2_igg_brochure.pdf.pdf (accessed 24 May 2020).

Disclaimer

The above is intended to serve as a rapidly-created, accessible source of information curated by medical students and healthcare professionals. It is for educational purposes only and is not a complete reference resource. It is not professional medical advice, and is not a substitute for the discretion, judgment, and duties of healthcare professionals. You are solely responsible for evaluating the information above.