CDC: False-negatives common with rapid flu tests

Healthcare providers should not rely entirely on rapid flu tests when determining if patients have influenza.

CDC: Health Care Providers Shouldn't Rely on Rapid Flu Tests
CDC: Health Care Providers Shouldn't Rely on Rapid Flu Tests

HealthDay News -- Healthcare providers should not rely entirely on rapid flu tests when determining if patients have influenza, according to U.S. health officials

Rapid flu tests used in many clinics are showing that patients do not have the flu when in fact they do (false negative), according to Angela Campbell, MD, MPH, a medical officer in the respiratory diseases branch of the CDC, NBC News reported.

Rapid influenza diagnostic tests (RIDT) produce results within 15 minutes, but false negative results are more likely during influenza season when disease prevalence is relatively high.

Sensitivities of rapid flu tests range from 10% to 80% compared with other more accurate tests like viral culture or reverse transcription polymerase chain reaction (RT-PCR) that take longer to produce results, according to the CDC. Specificities range from 85% to 100%.

"Clinicians should realize that a negative rapid influenza diagnostic test result does not exclude a diagnosis of influenza in a patient with suspected influenza," the CDC wrote in it's summary of Influenza Antiviral Medications for the 2013-2014 season.  "When there is clinical suspicion of influenza and antiviral treatment is indicated, antiviral treatment should be started as soon as possible without waiting for results of additional influenza testing."

Flu is now widespread in 41 states and the H1N1 strain is causing 99% of confirmed cases, the CDC said in its weekly flu report.

Healthcare workers should be ready to treat patients for the flu even if the first test is negative, the agency emphasized. Laboratory confirmation is not necessary to start antiviral treatment, as current recommendations state treatment should be started as soon as possible after illness onset, and preferably within 48 hours.

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