Your child has a fever, cough, runny nose, body aches and chills.
Should you rush them to your pediatrician for a flu test?
Diagnosing the Flu with a Flu Test
While you may want to seek medical attention, depending on your child’s age and how sick they are, believe it or not, you don’t need a flu test to get diagnosed with the flu.
“If your doctor needs to know for sure whether you have the flu, there are laboratory tests that can be done.”
CDC on Diagnosing Flu
A flu test is an option though.
Is it a good option?
A necessary option?
“Most people with flu symptoms are not tested because the test results usually do not change how you are treated.”
CDC on Diagnosing Flu
While a diagnosis of the flu can be made clinically, based on your symptoms, a flu test can be a good idea:
- to help determine the cause of an outbreak (mostly if there aren’t already a lot of flu cases in your area)
- if someone is at high risk for flu complications
In general though, most people do not need a flu test, especially during the active part of flu season.
What’s the problem with doing a flu test?
“In January 2017, the FDA reclassified antigen-based RIDT systems into class II. This reclassification was to help improve the overall quality of flu testing. The reclassification was prompted, in part, by recognition that the poor sensitivity of some of antigen-based RIDTs resulted in misdiagnosed cases, and, according to anecdotal reports, even death.”
FDA on CLIA-Waived Rapid Flu Test Facts
Mostly, they are neither as accurate nor as easy to interpret as most folks think, even the newer versions of these tests.
Have you ever heard someone say that they tested positive for both flu A and flu B?
When a flu tests is positive for both A and B flu strains, it invalidates the test. They may have had either flu A or flu B or neither, but they almost certainly didn’t have both.
The antigen-based rapid flu tests that most doctors and clinics use, which give results in 10 or 15 minutes, are also prone to both false positive (you don’t really have the flu, even though your test was positive), and more commonly, false negative (you actually do have the flu, even though your test was negative) results, depending if flu is active at the time.
Other flu tests are available, but are more expensive and take longer to get results, so aren’t used as often. These include “rapid” nucleic acid detection based tests that can be done in a doctor’s office, rapid nucleic acid detection based tests and rapid influenza diagnostic tests that are done in a central lab, PCR tests, and viral cultures.
So why do so many people rush to the doctor to get a flu test?
Many think that if they are positive, then they can take Tamiflu or another flu medicine and get better faster.
The problem with thinking like that is that few people actually need to take Tamiflu, as at best, it only helps you get better about a day quicker than if you didn’t take it. That’s why the recommendations for Tamiflu say to reserve it for children under two to five years of age and others who might be at high risk for flu complications.
Since most other people don’t need to take Tamiflu, they don’t necessarily need a flu test or a definitive diagnosis of the flu. Again, even if they did need Tamiflu, the diagnosis of the flu could be made clinically.
And even more importantly, a negative flu test doesn’t necessarily mean that you don’t really have the flu, especially if you have classic flu symptoms in the middle of flu season. Again, a negative flu test could be a false negative.
“RIDTs may be used to help with diagnostic and treatment decisions for patients in clinical settings, such as whether to prescribe antiviral medications. However, due to the limited sensitivities and predictive values of RIDTs , negative results of RIDTs do not exclude influenza virus infection in patients with signs and symptoms suggestive of influenza. Therefore, antiviral treatment should not be withheld from patients with suspected influenza, even if they test negative.”
CDC on Guidance for Clinicians on the Use of Rapid Influenza Diagnostic Tests
Have you ever had a negative flu test and the doctor still gave you Tamiflu? Then why did they do the test?
Diagnosing the Flu Without a Flu Test
If the results of flu testing aren’t going to change how you are treated, then you probably don’t need to have the flu test done in the first place.
Plus it saves you from having a swab stuck up your nose.
But kids should have flu tests, right?
Although rapid flu tests might be a little more accurate in kids than adults, it is not by much, so you are left with the same issues.
A positive test might reassure you that it really is the flu, but your child could still have the flu if their test is negative. A diagnosis and treatment decision can be made clinically, without a flu test, remembering that most older, healthy kids don’t need to be treated with Tamiflu.
More on Flu Tests
- When To Bring Your Child With The Flu Into The ER
- Influenza (flu) and your baby
- CDC – The Flu: What To Do If You Get Sick
- CDC – Diagnosing Flu
- CDC – Information for Clinicians on Influenza Virus Testing
- CDC – Guide for considering influenza testing when influenza viruses are circulating in the community
- CDC – Algorithm to assist in the interpretation of influenza testing results and clinical decision-making during periods when influenza viruses are circulating in the community
- CDC – Algorithm to assist in the interpretation of influenza testing results and clinical decision-making during periods when influenza viruses are NOT circulating in the community
- CDC – Guidance for Clinicians on the Use of Rapid Influenza Diagnostic Tests
- FDA – CLIA-Waived Rapid Flu Test Facts
- FDA – Public Health Perspective on Potential Benefits and Risks of OTC Influenza Diagnostics
- Study – Performance of rapid influenza diagnostic tests (QuickVue) for Influenza A and B Infection in India
- Study – Performance of Rapid Influenza Diagnostic Testing in Outbreak Settings
- How Accurate Are Rapid Flu Tests?
- Colds, Flu, and Other Respiratory Illnesses in Adults
Last Updated on November 25, 2018 by Vincent Iannelli, MD