FDA Compares Performance of COVID-19 Diagnostic Tests

Damian McNamara

September 17, 2020

Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center.

The US Food and Drug Administration (FDA) revealed comparative performance data for 55 molecular diagnostic COVID-19 tests that the agency approved under an Emergency Use Authorization protocol.

Patients, physicians, and laboratories can use the online data to get a better understanding of how each authorized commercial assay compares with a reference panel the FDA developed.

Test manufacturers are expected to compare their products in development with the benchmark data. But there is more to the story.

"Reference panels can be used in many ways to support test development and authorization, but most importantly, they are a powerful tool in monitoring test performance and ensuring that Americans have access to diagnostics they can trust," Jeff Shuren, MD, JD, Director of FDA's Center for Devices and Radiological Health, said in a news release.

The FDA compares each test's "limit of detection." This threshold reflects the minimum amount of virus that must be present in a sample for the test to yield a positive result, reflecting the sensitivity of the assay.

The agency stated, "the data gives laboratories, healthcare providers, and patients a new resource on the relative performance of available tests to better inform which tests they choose to use."

How Useful for Clinicians

"This test comparison is not something that most doctors will use, as they will use the tests that are at their disposal. However, physicians who play a role in deciding which tests their facility utilize will find this information to be useful, as will laboratory staff," Tony Zitek, MD, of the Department of Emergency Medicine at Kendall Regional Medical Center in Miami, Florida, told Medscape Medical News.

He said it makes sense that the FDA is comparing tests based on the limit of detection (LoD). "You would expect a test with the lowest limit of detection to have the highest sensitivity. That being said, the analytic sensitivity in the laboratory often does not perfectly correlate with the clinical sensitivity. The COVID-19 tests I have reviewed have high analytic sensitivity but moderate or low clinical sensitivity," said Zitek, author of the review article, "The Appropriate Use of Testing for COVID-19."

In clinical practice, the limit of detection "does not necessarily translate to better test quality," he added.

Furthermore, Zitek said, "determining the degree to which a person with COVID-19 is contagious is complicated and does not directly relate to the results of these tests. Patients can be contagious and have negative tests, and patients with positive tests may not be contagious. It is possible that a test with a very low LoD may continue to be positive for a longer period of time after the patient has recovered (even if the patient is not contagious)."

The SARS-CoV-2 Reference Panel Comparative Data features companies that provided the required data alphabetically, from Abbott Diagnostics to Zymo Research Corporation. Physicians and patients can also search by keyword.

Some manufacturers have not yet provided data, or their submission remains under review. The agency plans to continue evaluating COVID-19 test performance on an ongoing basis.

"By providing this panel to both commercial and laboratory test developers and evaluating the data we receive, we are able to gain valuable insight into the comparative performance of different authorized molecular diagnostic tests under the same conditions," Shuren added in the release.

In a recent commentary for Medscape Medical News, William P. Hanage, PhD, of Harvard T.H. Chan School of Public Health in Boston, Massachusetts, points out that a perfect COVID-19 test — one with 100% sensitivity and specificity — should not be the only goal. The speed of assay results matters as well, and in some cases highly specific but less sensitive testing could prove invaluable in reducing transmission of SARS-CoV-2.

Dr Zitek has disclosed no relevant financial relationships.

US Food and Drug Administration: SARS-CoV-2 Reference Panel Comparative Data

Damian McNamara is a staff journalist based in Miami. He covers a wide range of medical specialties, including infectious diseases, gastroenterology and dermatology. Follow Damian on Twitter:  @MedReporter

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