COVID-19 Evidence Alerts
from McMaster PLUSTM

Current best evidence for clinical care (more info)

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Diagnosis Homza M, Zelena H, Janosek J, et al. Covid-19 antigen testing: better than we know? A test accuracy study. Infect Dis (Lond). 2021 May 14:1-8. doi: 10.1080/23744235.2021.1914857.
Abstract

BACKGROUND: Antigen testing for SARS-CoV-2 is considered to be less sensitive than the standard reference method - real-time PCR (RT-PCR). It has been suggested that many patients with positive RT-PCR 'missed' by antigen testing might be non-infectious.

METHODS: In a real-world high-throughput setting for asymptomatic or mildly symptomatic patients, 494 patients were tested using RT-PCR as well as a single lateral flow antigen test (Ecotest, AssureTech, China). Where the results differed, virus viability was evaluated by cell culture. The test parameters were calculated with RT-PCR and RT-PCR adjusted on viability as reference standards.

RESULTS: The overall sensitivity of the used antigen test related to the RT-PCR only was 76.2%, specificity was 97.3%. However, 36 out of 39 patients 'missed' by the antigen test contained no viable virus. After adjusting on that, the sensitivity grew to 97.7% and, more importantly for disease control purposes, the negative predictive value reached 99.2%.

CONCLUSIONS: We propose that viability testing should be always performed when evaluating a new antigen test. A well-chosen and validated antigen test provides excellent results in identifying patients who are shedding viable virus (although some caveats still remain) in the real-world high-throughput setting of asymptomatic or mildly symptomatic individuals.

Ratings
Discipline / Specialty Area Score
Hospital Doctor/Hospitalists
Internal Medicine
Pediatrics (General)
Public Health
Infectious Disease
Pediatric Emergency Medicine
Emergency Medicine
Comments from MORE raters

Hospital Doctor/Hospitalists rater

Confirmation with other antigen test kits would be needed.

Pediatric Emergency Medicine rater

If the gold standard is PCR, then the sensitivity and specificity ought to be reported accordingly rather than excluding a subset based on “virus viability”.