Rapid Influenza Tests Need To Be More Reliable, FDA Says

June 11, 2014

The rapid influenza detection tests (RIDTs) that physicians use in their office need to become more accurate to keep pace with mutating influenza bugs, according to the US Food and Drug Administration (FDA).

The FDA has a plan to make the 15- to 30-minute tests more precise: Put them in a different class of medical devices that the agency can more tightly regulate. It published a proposal to do just that in the Federal Register last month.

The dozen or so RIDTs on the market represent enzyme immunoassay technology, which spots antigens to the seasonal influenza virus in clinical specimens. The tests are high in specificity, meaning that patients who test positive usually harbor the virus.

However, the tests have had a longstanding problem with low sensitivity, and therefore too many false-negatives, the FDA said in its proposal. False-negatives can lead to misdiagnosed patients who risk serious illness or even death if they are not promptly treated. In addition, such misdiagnoses generate false epidemiological data that may send public health authorities down the wrong path in fighting influenza.

The pandemic A(H1N1) virus of 2009 underscored the unreliability of RIDTs and raised the fear that the tests were even less likely to yield accurate negatives as influenza viruses mutated over time.

"The tests picked up only a minority of the [pandemic] infections," said Paul Auwaerter, MD, clinical director of the Division of Infectious Diseases at Johns Hopkins University School of Medicine in Baltimore, Maryland. "That's what engendered this whole issue."

Testing the Test

Last year, Dr. Auwaerter served temporarily on an FDA advisory committee for microbiology devices that recommended 4 ways to improve RIDTs.

  • Set minimum sensitivity criteria.

  • Identify the best "comparator" test to determine the accuracy of RIDTs. A viral culture was once the gold-standard reference method, but the committee said any comparison also ought to include newer molecular-based assays.

  • Each year, RIDT manufacturers should gauge the accuracy of their devices, using the latest influenza viruses in circulation to account for "evolutionary changes of the virus."

  • When a novel influenza virus threatens the public, as it did in 2009, manufacturers must subject it to RIDT testing as soon as samples are available.

Within the FDA, these regulatory fixes are considered "special controls" because they are device-specific. However, the agency cannot impose them on RIDTs right now because the agency approved them as lower-risk class I devices, which are subject to only general controls designed for all medical devices. Examples of general controls include good manufacturing practices and adverse event reporting.

Special controls are allowed, however, for higher-risk class 2 devices. Accordingly, the FDA advisory committee recommended reclassifying RIDTs into this higher tier.

The proposed regulations on RIDTs published by the FDA on May 22 call for the reclassification and special controls recommended by the advisory committee. The public has 90 days from the date of publication to submit comments.

Dr. Auwaerter told Medscape Medical News he did not hear "terribly negative" comments from RIDT manufacturers last year about the solutions concocted by the advisory committee. "They realize that people won't buy their tests if they don't work," he said.

A complete text of the proposed RIDT regulations is available on the Federal Register Web site.

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