Flu Test: How and When to Get Tested
Key takeaways:
The most common and fastest type of flu test is called a rapid influenza diagnostic test (RIDT). This test detects antigens specific to the virus.
RIDTs are more common, but they’re less accurate than other flu tests. Rapid molecular assays and reverse transcription polymerase chain reaction (RT-PCR) tests are more accurate.
Typically, you’ll go to a healthcare professional to be tested for the flu.
Table of contents
The flu is a contagious infection caused by the influenza virus. Some flu seasons are worse than others. In a bad year, for example, the flu can sicken as many as 41 million people in the U.S.
If you have a cough, sore throat, or fever, you may be wondering if you have the flu. The only way to find out for sure is to take a flu test. Within minutes, you may know if you have the flu or not. Knowing this can help you determine what kind of treatment is best.
Is there a test for the flu?
Yes, there are several flu tests available. The most common and fastest type of flu test is called a rapid influenza diagnostic test (RIDT). An RIDT detects the parts of the flu virus — called antigens — that cause you to feel sick.
Search and compare options
You’ll typically get results in about 10 to 15 minutes, but RIDTs aren’t as accurate as some other flu tests. If you have a positive RIDT, you can be pretty sure that you have the flu. But if the RIDT is negative, you still might have the flu: It just wasn’t detected by the test.
Other types of flu tests include:
Rapid molecular assays: These flu tests detect the genetic fingerprint of the flu virus. They’re more accurate than RIDTs. You’ll get results in about 15 to 30 minutes.
Reverse transcription polymerase chain reaction (RT-PCR): These also detect the genetic fingerprint of the flu virus. But they’re more accurate than both RIDTs and rapid molecular assays. RT-PCR tests are usually only done at hospitals or special laboratories. Results can take anywhere from 45 minutes to a few hours.
Immunofluorescence: This type of flu test uses a special microscope to detect flu viruses, so it won’t be available at all clinics. It takes about 2 to 4 hours to get results, and it has an accuracy similar to RIDTs.
Viral cultures: This type of flu test is the slowest, taking 1 to 3 days to get results. The test sample needs to be sent to a lab, where it’s grown and examined by experts. This type of test is usually only done for research purposes and can help experts find out which flu virus strains are circulating in communities.
How do healthcare professionals test for the flu?
A flu swab test is one of the most common methods of taking a sample for your flu test.
Typically, a special swab — usually similar to a long cotton swab — is used to take a sample from your nose or throat.
You don’t have to do anything special before having a flu test. Here’s what to expect:
To take a sample, the healthcare professional will first ask you to tilt your head back a bit. Then they'll gently insert the cotton swab into one nostril.
The swab will be left in place for a few seconds to soak up fluids.
The healthcare professional will slowly remove the swab while rotating it.
Then they’ll insert the same swab into your other nostril and repeat the process.
Home remedies for the flu: Learn about these natural treatments that may help you feel better faster from the flu.
How contagious is the flu? Find out more about how the flu virus is spread and how to protect yourself.
Tamiflu dosing: Read more about who should get Tamiflu and when it’s prescribed.
This type of flu test can be a little uncomfortable for some people. But don’t worry — it’s a temporary feeling that’ll quickly go away after the sample is collected.
How long does a flu test take?
The whole process of collecting a sample to test for the flu — from tilting your head back to having both nostrils swabbed — will take only 15 to 30 seconds. And, depending on the type of flu test used, you could receive your results in as little as 15 minutes.
A healthcare professional will also likely want to know more about your symptoms and medical history. This will help them recommend the best care plan for you.
Can you test for the flu at home?
At-home flu tests are available. For some of them, you’ll collect the sample at home and send it to a lab. But the FDA authorized its first at-home diagnostic flu test in February 2023. This test provides at-home results in about 30 minutes.
There are some things to know when it comes to at-home flu tests:
Some of these may be antigen tests. As mentioned above, antigen tests are less accurate than other flu tests. This means you may get a false negative result.
It can be hard to get a good sample when testing yourself. And without a good sample, your test results are less likely to be accurate.
You may need to wait for lab results. Since most at-home flu tests require you to send samples to a lab, you may not get your result for a few days.
If you do have the flu, you still need to see a healthcare professional. They’ll need to confirm your at-home test results in order to prescribe you any flu treatments, such as Tamiflu (oseltamivir).
Are flu tests accurate?
The accuracy of a flu test depends on the type of test and how long you’ve had symptoms before being tested:
Flu tests are most accurate when used sooner rather than later. For all types of flu tests, they’re most accurate if done as close to the start of your symptoms as possible, ideally less than 4 days.
RIDTs may be quick, but they’re not as accurate as other tests. They’re able to detect flu viruses between 50% and 70% of the time. If paired with a special reader device, they become slightly more accurate (75% to 80%). If you get a positive result from an RIDT, you have the flu. If it’s negative, you still might have the flu, but the test didn’t detect it.
Rapid molecular assays are much more accurate than RIDTs. They’re typically between 90% and 95% accurate.
RT-PCR tests are also very accurate flu tests. Some studies have even found them to be 98% accurate at detecting flu viruses.
Immunofluorescence tests aren’t as accurate as some others. According to the CDC, immunofluorescence tests have “moderate” accuracy, but an exact percentage isn’t provided. All we can say from this information is that this flu test is less accurate than rapid molecular assays and RT-PCR tests.
Flu test results
No matter which flu test you take, if you get a positive test result, there’s a good chance that you have the flu. If you get a negative result, it means that the virus wasn’t found in your sample. But as we discussed, it’s possible to get a false negative result. This may be possible if you have symptoms, a known exposure, or other factors that suggest you’re infected. A healthcare professional may use all of this information in determining the best course of action for you.
What should I do if I test positive for the flu?
If you test positive for the flu, a healthcare professional may prescribe you an antiviral medication, such as Tamiflu (oseltamivir) or Xofluza (baloxavir marboxil).
Keep in mind that treatment for flu is best when started within 2 days of the onset of symptoms. Besides getting started on any antiviral medications, you should also:
Stay away from other people as much as possible while you’re sick. You don’t want to spread the flu to others.
Cover your nose and mouth when you cough or sneeze. Wearing a face mask is helpful with this.
Wash your hands often with soap and water for at least 20 seconds. If you’re unable to access soap and water, use an alcohol-based hand sanitizer.
Clean surfaces at home. Clean any surfaces or items that multiple people touch (such as door knobs, handles, tables, and TV remote controls).
Stay home until you’re better. The CDC recommends staying home for at least 24 hours after your fever goes away completely.
When should I get a flu test?
Remember, flu tests are most accurate when done close to the start of symptoms. If you experience any of the following flu symptoms, it might be a good idea to get a flu test:
Fever or feeling like you have a fever
Chills
Coughing
Sore throat
A runny or stuffy nose
Muscle pain
Body aches
Headache
Feeling tired
Vomiting or diarrhea (more common in kids than adults)
It’s important to know that everyone’s flu symptoms are different. You may have some or all of these. But typically, flu symptoms come on quickly (compared to cold symptoms, which may get gradually worse over a few days).
If you experience any of the following symptoms, you should seek immediate medical care:
Shortness of breath
Chest pain
Extreme confusion or dizziness
Finding it extremely hard to wake up
Fainting or seizures
Not being able to urinate at all
A significant decrease in urination, or having dark urine
You should also see a healthcare professional if your symptoms get better and then get worse again. This could be a sign of complications developing from the flu.
Can you be tested for COVID-19 and other respiratory illnesses at the same time?
Currently, the FDA has authorized several tests that have the ability to detect multiple viruses at the same time. Instead of taking separate tests for each virus, this option allows you to take just one test to help identify what’s potentially causing your infection.
Some of these tests can look for flu viruses as well as COVID-19, respiratory syncytial virus (RSV), and several other respiratory infections. Others only test for flu viruses and COVID.
Frequently asked questions
If you think you have the flu, it’s a good idea to call a healthcare professional sooner rather than later. That’s because antiviral flu treatment is most effective when started within 48 hours of your symptoms starting. This treatment can help to shorten the number of days that you’re sick.
The flu is most contagious within the first 3 days after your symptoms appear. Most people remain contagious for up to a week. As a general rule, you’re no longer contagious once your symptoms improve and you feel well again.
Fever is a common symptom of the flu. But not everyone with the flu will get a fever. If you don’t have a fever but you have other symptoms of the flu, it’s still a good idea to get tested.
The bottom line
If you’ve got a cough, fever, or sore throat, you may be wondering if you have the flu or another respiratory illness. The best way to find out what’s making you sick is to visit a healthcare professional. They may decide to do a flu test while you’re at your appointment. A variety of tests are available, and many can provide results the same day. No matter what your test results are, it’s best to stay home until you’re feeling better to help prevent spreading viruses and germs to others.
Why trust our experts?
References
Centers for Disease Control and Prevention. (n.d.). Influenza specimen collection.
Centers for Disease Control and Prevention. (2023). Guide for considering influenza testing when influenza viruses are circulating in the community.
Centers for Disease Control and Prevention. (2024). About estimated flu burden.
Centers for Disease Control and Prevention. (2024). Diagnosis for flu.
Centers for Disease Control and Prevention. (2024). Overview of influenza testing methods.
Centers for Disease Control and Prevention. (2024). Signs and symptoms of flu.
Centers for Disease Control and Prevention. (2024). Treatment of flu.
Maignan, M., et al. (2019). Diagnostic accuracy of a rapid RT-PCR assay for point-of-care detection of influenza A/B virus at emergency department admission: A prospective evaluation during the 2017/2018 influenza season. Public Library of Science One.
U.S. Food and Drug Administration. (2023). FDA authorizes first over-the-counter at-home test to detect both influenza and COVID-19 viruses.
U.S. Food and Drug Administration. (2024). In vitro diagnostics EUAs - molecular diagnostic tests for SARS-CoV-2.
