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WHO Discourages Use of POC Coronavirus Immunoassays for Clinical Decision-Making

NEW YORK – The World Health Organization has recommended that new point-of-care immunodiagnostic tests for the coronavirus that causes COVID-19 should not be used for clinical decision-making. At present, the tests shouldn't be used outside research settings "until evidence supporting use for specific indications is available," the WHO said in a scientific brief on Wednesday.

Molecular PCR "testing of respiratory tract samples is the recommended method for the identification and laboratory confirmation of COVID-19 cases," the WHO said.

The organization added that before point-of-care immunodiagnostic tests can be recommended, "they must be validated in the appropriate populations and settings. Inadequate tests may miss patients with active infection or falsely categorize patients as having the disease when they do not, further hampering disease control efforts."

It noted that many diagnostic test manufacturers have developed and begun selling rapid assays for testing outside lab settings, in response to the growing COVID-19 pandemic and shortages of lab-based molecular testing capacity and reagents.

One type of rapid diagnostic test (RDT) detects the presence of viral proteins, or antigens, expressed in a sample from the respiratory tract by the virus that causes COVID-19.

"If any of the antigen detection tests that are under development or commercialized demonstrate adequate performance, they could potentially be used as triage tests to rapidly identify patients who are very likely to have COVID-19, reducing or eliminating the need for expensive molecular confirmatory testing," the WHO said.

However, several factors influence how well the test works, and its level of sensitivity might be expected to vary from 34 percent to 80 percent, based on experience with antigen-based RDTs for other respiratory diseases such as influenza, the WHO said. Comparable concentrations of influenza virus and the SARS-CoV-2 virus that causes COVID-19 are seen in respiratory samples, it added.

The WHO said that "half or more of COVID-19 infected patients might be missed by such tests, depending on the group of patients tested." False-positive results could occur if the antibodies on the test strip also recognize antigens of viruses other than COVID-19, such as from human coronaviruses that cause the common cold.

A second, more common type of rapid diagnostic test marketed for COVID-19 detects the presence of antibodies in the blood of people believed to have been infected with COVID-19. WHO said that based on current data, it doesn't recommend the use of antibody-detecting rapid diagnostic tests for patient care, but it "encourages the continuation of work to establish their usefulness in disease surveillance and epidemiologic research."

"Tests to detect antibody responses to COVID-19 in the population will be critical to support the development of vaccines, and to add to our understanding of the extent of infection among people who are not identified through active case finding and surveillance efforts, the attack rate in the population, and the infection fatality rate," the WHO said. "For clinical diagnosis, however, such tests have limited utility because they cannot quickly diagnose acute infection to inform actions needed to determine the course of treatment."

To inform its policy on the use of immunodiagnostic rapid tests for COVID-19, the organization is working with a "global laboratory expert network, and closely reviewing the results of laboratory and clinical studies planned and implemented by reference laboratories, academic groups, and non-governmental organizations," the WHO said.

It is already evaluating COVID-19 molecular diagnostic products for quality and safety through the WHO Prequalification Emergency Use Listing Procedures and through a collaboration with the Foundation for Innovative New Diagnostics.