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Early Flu Tests & How They Work | Medical Minute Monday Ep. 5

March 4, 2020


Hey there! Stan the Medical Minute Man here, back with
your weekly Medical Minute Monday! To better prepare you for the flu season,
we’re discussing rapid influenza tests today. When diagnosing the cause of a disease, I
think we’d all agree that earlier is better. Rapid influenza detection tests, or RIDTs,
are tests that…well…rapidly detect influenza. These are antigen detection assays, similar
to rapid Strep. tests, and they typically yield results in 10-30 minutes. Some RIDTs are even cleared for bedside use,
which means that access to a laboratory is not needed. The best method for collecting a sample is
usually a nasal aspirate, which is when saline is injected into the nostril and then suctioned
out. Nasal swabs are faster, easier, and more comfortable
for the patient, so they’re more common. Throat swabs can be used, if necessary, but
they are considered to be the inferior method for collecting the sample. Fast, minimally invasive, and accessible. These tests sound great, so why do we still
have slower tests available? Rarely do we see an increase in speed without
some form of cost, and RIDTs are no exception. The first disadvantage is that some RIDTs
don’t differentiate between influenza A and B, and none of them detect influenza C.
Fortunately, most RIDTs will differential between influenza A and B, and the inability
to test for influenza C isn’t a major concern because this strain usually causes mild symptoms
and doesn’t result in epidemics. The second disadvantage is specific to influenza
A. Influenza A has hundreds of subtypes, such
as H1N1, but an RIDT won’t tell you what subtype the patient has. Lastly, and perhaps the most significant disadvantage
of RIDTs, is that they have sub-optimal test sensitivity. This means that false negatives are common,
especially when influenza activity is high. False positives are less likely but still
occur, especially when influenza activity is low. The big picture? RIDTs are convenient, fast, and especially
beneficial to clinicians working in remote areas where advanced techniques are not readily
available. However, they have a higher chance of false
negatives and positives, some provide incomplete information regarding the influenza strain,
and no information regarding the influenza A subtype is provided. With this in mind, don’t be surprised to
see your clinician prescribe antivirals to treat influenza despite a negative RIDT, this
is especially true if influenza is prevalent in your community. I hope you enjoyed this week’s Medical Minute
Monday! Now you know a thing or two about rapid influenza
diagnostic tests, but how are you with antipyretics? Fever is often seen with influenza, so be
sure to check out our antipyretics Medical Minute! Do you want to see more influenza-related
Medical Minutes? Let me know by leaving a comment below. I’ll see you all next Monday for a review
of funduscopy!

1 Comment

  • Reply Daniel Hamilton December 25, 2018 at 10:18 am

    In recent years in the U.S. I think the number ranged from somewhere between 100,000 to 120,000 deaths from flu ๐Ÿ™ and the recent legislature statistical data gathered by DSHS for the fiscal year stated that the number of people refusing to be inoculated for some diseases is on the rise. 12/25/2018

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