Study Supports ‘Judicious’ Use of COVID-19 Rapid Antigen Tests

NEW YORK (Reuters Health) – Most COVID-19 rapid antigen tests – also known as lateral-flow antigen tests – perform to a high standard, with good sensitivity and excellent specificity, according to a head-to-head comparison of six such tests.

The results “support the judicious use” of lateral-flow devices (LFDs) for rapid antigen detection, “not to replace PCR testing, but to supplement current testing capacity and rapidly identify infected individuals in situations in which they would otherwise go undetected,” report Dr. Rui P. Galao and colleagues at King’s College London, in U.K., in a paper in The Lancet Microbe.

Unlike PCR tests, which involve complex lab equipment and highly trained staff, lateral-flow tests can be processed on the spot and provide rapid results.

These rapid diagnostic tests play a major role in SARS-CoV-2 mass community and healthcare testing, and understanding their capabilities and limitations is essential for successful implementation, Dr. Galao and colleagues say.

They evaluated six commercial LFDs – Innova Rapid SARS-CoV-2 Antigen Test, Spring Healthcare SARS-CoV-2 Antigen Rapid Test Cassette, E25Bio Rapid Diagnostic Test, Encode SARS-CoV-2 Antigen Rapid Test Device, SureScreen COVID-19 Rapid Antigen Test Cassette, and SureScreen COVID-19 Rapid Fluorescence Antigen Test – and assessed their correlation with infectious virus culture and PCR-cycle threshold (Ct) values.

In line with previous data, the tests delivered an overall sensitivity of 65% to 89% in comparison with PCR testing, with sensitivity increasing to greater than 90% for most tests for samples with Ct values below 25, the researchers report.

Among the Innova, Encode and SureScreen tests, sensitivity increased to at least 95% when compared with samples that were infectious in vitro, with viral titer in the specimens correlating with Ct values.

“This study, to our knowledge, provides the most comprehensive comparison of antigen LFDs and infectivity to date, showing a clear relationship between Ct values, quantitative culture of infectious virus, and antigen LFD positivity, with the tests used in each analysis delivering reliable identification of infectious clinical samples,” Dr. Galao and colleagues say.

“The positive samples included in this study were representative of those encountered by the diagnostic laboratory at St Thomas’ Hospital, including from healthcare workers and their household contacts, asymptomatic individuals undergoing unrelated hospital treatment, and individuals with mild to severe COVID-19. Given the breadth of samples, we expect the findings from this study to apply to a wide range of infection scenarios,” they write.

They note that while these rapid antigen tests are easy to use, the correct sampling, reading, and interpretation of the result are “essential to their success in mass screening situations. In particular, mass screening programs need to consider training and familiarity with swabbing when deploying devices to the general public as compared with a trained healthcare worker in a hospital or clinical setting. It is also easy to underestimate the importance of correctly recognizing a positive band. We found that some tests gave clearer results than others.”

In June, the U.S. FDA issued a safety communication ( expressing “significant concerns” about the performance of the Innova Medical Group SARS-CoV-2 Antigen Rapid Qualitative Test and advising clinicians to stop using it for diagnosis.

The authors of the current study point out that rapid tests will also need to be continually reassessed in the context of emerging SARS-CoV-2 variants.

Summing up, the study team says although sensitivity is lower than with PCR-based testing, “the rapid turnaround of these LFD tests, their versatility in terms of cost and portability, and their utility in disrupting transmission chains originating from infectious asymptomatic individuals could outweigh the risk of missing positive cases.”

Funding for the study was provided by King’s Together Rapid COVID-19, Medical Research Council, Wellcome Trust, Huo Family Foundation, UK Department of Health, National Institute for Health Research Comprehensive Biomedical Research Centre.

SOURCE: The Lancet Microbe, online June 30, 2021.

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