Everything you need to know about the rapid influenza test – a good read for both before and after you got tested!

What is a rapid influenza test?

Most of the tests available (I will not go into the different brand names available because there are so many), are based on the histochemical colouring of the samples containing the influenza virus antigen.
What I’m trying to say is that when you place some snot containing influenza on one end of the test, a chemical reaction occurs as the antigen binds to the antibody found in the test to indicate a positive result on the other end.

So why are there two stripes on the test board?

Rapid tests always show two stripes: one of them represents the control. The control stripe must be there. If it isn’t there, something is wrong with the test you took.

Is the flu test a PCR test? Just like the COVID-19 tests?

Do not get confused. The flu test is not a PCR test. PCR tests check for the presence of genetic material belonging to the virus and this is usually only done in labs. The influenza rapid test is a rapid antigen test.
This is also why it is less accurate, as you will learn below.

Home tests or office tests?

At first all these rapid tests were only available at the doctor’s office or in laboratories.
But COVID-19 allowed big pharmaceutical companies to expand, and they started selling these rapid kits for people to buy and take home. So that same test that your doctor would do at his/her office, is now available for you to take home.
A medical professional who does several of these tests a day may possibly be better skilled than you at testing you and taking their test may possibly reveal results that are more reliable, but more about this later.

Does the rapid flu test also check the type of flu I am suffering from?

Yes. I am sure you have already read the mythological chapter about the influenza virus that I posted on this website (link here) where I explained about the two main types of influenza: A and B. Most rapid tests are able to distinguish between the two.
Does this really matter in practice? Not really.

So, what are the benefits of taking a rapid flu test?

The results of this test, whether it is positive or negative, is very significant.
For example – a teenage girl visited my office the other day with high fever and shivers. About a year ago she had a kidney infection, despite no signs or symptoms during urination. Her physical examination was normal except for mild redness in her throat. We performed a rapid flu test which came back positive. Great! The source of her fever was influenza and not a kidney infection. What a relief!
Another example – a similar story with an 18-months old baby. The mother tested her for flu at home and the result was negative so she came to my office. Her physical exam revealed an ear infection. Nice!

What is the message I’m trying to convey? The positive or negative test result help when you put things into clinical context.
You got a positive result and it makes sense within the clinical scenario? The patient has influenza, will be ill for the next few days and is not likely to be suffering from a bacterial infection right now so there is no need to prescribe them with antibiotics. However, since influenza can also have its complications, it is important to point these out to the patient and make sure they are able to identify such complications and seek medical attention as needed (for example: secondary fever).
You got a negative result and it makes sense within the clinical scenario? Continue looking for the cause of the child’s symptoms together with your physician. It could be a bacterial infection that requires more attention.
Everything, however, has its potential drawbacks and it is important to understand them before taking this test.

What are the drawbacks of the rapid flu test?

Sensitivity of the test – a test’s sensitivity is the chances that a test result will indicate ‘positive’ if a person has the flu. Ideally, we would have wanted the test to be very accurate, that is, a sensitivity of 100%. Unfortunately, the quality of the home tests in the market these days combined with the manner in which people tend to perform it (placing the swab on the tip of their nose only for a second), makes the test’s sensitivity very low. And then people who actually have the flu get a negative result and will sometimes start antibiotics because he/she and their physician think they have sinusitis (for example) even though the flu test would have been positive had it been more sensitive.
How can sensitivity of a test be improved? By choosing a good quality test kit (unfortunately I can’t really tell you which of the kits out there are the good ones) and trying to swab properly. I always tell my patients – make sure the swab is wet when you take it our of your nose!
Lack of understanding of the clinical situation relevant to the test – what do I mean by this? Bear with me for a minute. Little Emily came to visit my office after her test indicated she was positive for the flu when her entire family had the flu, too. Her mother called the nurse several times over the course of a few days because her daughter wasn’t well, but she was told repetitively that she needs to wait because the girl simply has the flu. After 6 days of illness, a chest x-ray was finally performed and it revealed a large pneumonia. That is why I always say, even if your rapid flu test indicates you are positive for the flu, it does not necessarily mean that you don’t need to seek medical attention. See your doctor so that you can make a joint decision regarding your specific clinical case and assess whether a complication has developed. Keep in mind that many times what starts of as the flu ends as a bacterial pneumonia in elders and an ear infection in younger patients.
In summary, the only way to really make proper use of this test is to perform it in the most reliable way and take it within clinical context.

Do I recommend the rapid flu test?

Absolutely. Knowledge is power.
When a person has typical signs and symptoms of the flu, I always recommend taking the rapid flu test as it can have a truly significant impact on management.
But I do not recommend taking the test and staying at home. Regardless of whether the result is positive or negative, I recommend seeing your doctor, just the same way as you would had you not taken the test.
Allow your doctor to take the test result and decide whether your clinical manifestations are in line with the result and whether further investigation or management are required.
Additionally, if your doctor has better quality kits at his/her office then I suggest you get tested there, by a healthcare professional who is skilled at performing the test so that your results are more reliable and your diagnosis more accurate.

What other types of rapid tests are available?

The rapid streptococcal test has been in the market for years. It is a very helpful tool for lots of pediatricians. Find out more about the rapid strep test in the following link.
What else? COVID-19, of course!
And the test.
Respiratory viruses – I used to have a rapid RSV test at my office (read more about RSV here) and there are rapid tests for other respiratory viruses as well.
There are also rapid tests for stool – most outpatient offices would rather avoid these because of how stinky it can get.
In the future our kids will just have to walk into the doctor’s office and place some snot in a little test tube and their doctor will be able to tell the name of the respiratory virus they have.

In summary, all rapid tests and especially the rapid influenza test are a very important auxiliary tool for pediatricians and parents. But it is important to use these tests wisely and properly, so as not to miss an important diagnosis.
Good luck!