Find Out When To Trust Rapid Flu Tests

Rapid influenza tests, which often produce results in 15 minutes or less, can be extremely useful in an emergency department, but you need to be aware of the diagnostic tool’s limitations.A recent review of research concluded that the tests are very accurate in diagnosing the flu but less so when it comes to ruling it out. What does that mean for patients who present with typical flu symptoms but test negative?

If a patient with influenza symptoms tests positive with a rapid influenza diagnostic test (RIDT) in your ED, you can confidently assume they have the flu and begin treatment and infection-control measures. If the result is negative, though, you probably should order additional testing, according to a study recently published in the Annals of Internal Medicine.

Researchers note that positive results are unlikely to be false positives, but “a negative result is unreliable and should be confirmed by using culture” or reverse transcription polymerase chain reaction (RT-PCR). Across the 159 published studies researchers reviewed, they found specificity to be more consistent than sensitivity. Specificity ranged from 50.5% to 100% while sensitivity ranged from 4.4% to 100%. Overall, the pooled sensitivity for all RIDTs was 62.3% and specificity was 98.2%. Pooled sensitivity was higher in children than adults. In addition, RIDTs were better at detecting influenza A than influenza B.

If the RIDT came back positive, should you administer antiviral therapy? According to another meta-analysis of 74 studies on the benefits of oseltamivir, zanamivir, and amantadine, treatment with some antivirals may be better than no treatment in certain high-risk populations.

Researchers concluded that therapy with oral oseltamivir and inhaled zanamivir may provide a net benefit. Oral oseltamivir may reduce mortality, hospitalization, and duration of symptoms in high-risk populations. “This highlights the potential positive effect of earlier rather than later administration of oseltamivir on death in hospitalized patients and suggests that pregnant women, children, and patients who are immunocompromised may also benefit from treatment,” according to the study’s primary conclusions. In addition, researchers found that inhaled zanamivir may shorten symptom duration and result in fewer hospitalizations, but it appears to be associated with more complications than no treatment.

View other topics in this week's edition of Pertinent Practice Pearls (free for everyone):

• For Many Women, No ‘Elephant Sitting on Their Chest’ with MI
• Toothaches Create New World of Pain for EDs
• Opioid Prescriptions from ED Less Likely to Result in Fatalities

View related topics in EB Medicine's publications:

• Pediatric Influenza In The Emergency Department Setting (free for subscribers)
• Influenza: Challenges In Diagnosis And Management In The Emergency Department (free for subscribers)