Should I test for flu at home if I have the sniffles?

You are “coming down with something”. Maybe you have a scratchy throat and body aches. You have an old, combination flu/COVID rapid antigen test in the cupboard.

Should you use it to see if you have the flu? Will it detect the “super-K” flu you’ve heard about? Or is it worth seeing a doctor for a test instead?

Here’s what to know about testing for flu at home.

Remind me, how do we test for flu?

There are two main ways to test for flu.

The reverse transcriptase-polymerase chain reaction test is known as RT-PCR or, more commonly, just PCR. This is what your GP orders after taking a swab of your nose and back of the throat. This test detects viral genetic material.

But rapid antigen tests or RATs are the type you do at home. These detect particular viral proteins (antigens) in your saliva or nasal secretions.

The Therapeutic Goods Administration lists RATs currently approved in Australia to detect respiratory viruses.

You can check your test against the list. This includes tests that detect various combinations of influenza (types A and B), respiratory syncytial virus (RSV), adenovirus (listed as ADV) and COVID.

Which test is best?

Both types of tests have their pros and cons. So here are some things to consider.

Speed

RATs are quick and you can do them at home. Once the sample is in the device, you will generally have your result in 15–20 minutes. You won’t need to make and attend a GP appointment. An at-home test means you are also not inflicting your germs on the GP, staff or other patients in the waiting room.

A PCR test takes longer. First you have to wait for a GP appointment. Then, you may have to wait several days for the results.

Cost

The cost of both tests can differ. A combination flu/COVID RAT can cost a few dollars, less per test if you buy in packs of five or more.

You would not usually be charged for a PCR test in Australia. However, if your doctor does not bulk bill, you will have to pay an out-of-pocket fee for the medical appointment itself.

Accuracy and the super-K variant

PCR tests are more accurate than RATs, and can detect a viral infection when your viral load (the amount of virus present) is much lower that what a RAT can detect. This is because the PCR process copies a section of the viral genome many times to make it more easily detectable.

So a negative RAT is no guarantee you don’t have the flu. If your symptoms continue and you are concerned, a PCR will provide a more accurate answer.

But can RATs detect new variants of the flu virus? Fortunately, RATs detect “highly conserved” proteins. These are proteins that tend to be stable between different variants. A new variant should not interfere with the sensitivity of the RAT – its ability to correctly detect the flu.

So it’s likely that a flu RAT can detect the new H3N2 subclade K influenza variant, dubbed “super-K”, although no data have been published on this yet.

Read more: When is the best time to get your flu shot? 2 infectious diseases experts explain

What if I’m at high risk?

People 65 or older, young children, pregnant women, and people taking immunosuppressive medications (such as, transplant recipients, or those having chemotherapy for cancer) are at greater risk of having more serious illness if they catch the flu.

In these higher-stakes situations, it might be better to see a GP as they can prescribe anti-flu drugs as a precaution.

These drugs may reduce the severity and duration of illness, and the risk of complications and hospitalisation associated with the flu.

If you decide to see your GP, let the surgery know you have symptoms. You may need to do an online consultation or wear a mask in the waiting room.

Are old RATs OK?

Before using a RAT that has been sitting in your cupboard, ensure it is within its use-by date and has been stored appropriately. If you have refrigerated the test, leave it at room temperature for about 30 minutes before using, otherwise it won’t work properly.

I’ve written previously about other do’s and don’ts of using RATs, including how to avoid sampling snot and how best to dispose of the test.

To detect flu it’s best to test within three to four days of symptoms starting. At this point the viral load will be highest and the test will be most accurate.

Read more: 15 things not to do when using a rapid antigen test, from storing in the freezer to sampling snot

In a nutshell

If you have symptoms of a respiratory illness, and you want to see what you have, using a RAT is a good idea. That’s as long as the test has not expired, has been stored correctly and you are not in a high-risk group.

If it’s likely flu could be more serious for you (or someone you may be in contact with), a GP appointment may allow you to access anti-viral medications to reduce your risk of severe illness, and a PCR test would offer a more accurate diagnosis.