Flu (Influenza) Test
Reviewed
Also called: rapid flu test, influenza antigen test, rapid influenza diagnostic test, RIDT, Flu PCR, Type A and B Antigen Detection
Most flu tests check a sample of fluid from your nose or throat to find out if you're infected with a flu virus.
Specimen: Nasopharyngeal swab, nasal aspirate or wash, conjunctival swab, sputum, bronchoalveolar lavage (BAL), or self-collected nasal swab (for at-home tests).
Why this test may be ordered
- To determine if your respiratory symptoms are caused by influenza A or B, especially if you are at high risk for serious complications.
- To help your healthcare provider decide if antiviral medicine is appropriate.
- To monitor flu and COVID-19 outbreaks in the community (public health use).
Preparation and collection
You don't need any special preparations for a nasopharyngeal swab, a nasal aspirate or wash, or a conjunctival swab. If you get a BAL and/or bronchoscopy, you may be asked to fast (not eat or drink) for up to twelve hours before the test. You may also be asked to stop taking certain medicines. But don't stop taking any medicines unless your provider tells you to.
A health care professional will insert a long swab into your nostril until it reaches your nasopharynx (the upper part of your throat). They will then rotate the swab for 10 to 15 seconds, remove it, and test that sample for signs of influenza A and B.
If your throat or nose is swabbed, you may feel a gagging sensation or a tickle. These effects are temporary. There is very little risk to having a bronchoscopy or a BAL. Serious complications are rare, but they may include bleeding in the airways, infection, or a pneumothorax (collapse of part of your lung).
Understanding results
The results of your flu test tell you if signs of influenza A or B virus were found in your sample. Your results are usually described as "positive" or "negative."
- Positive: A positive result means you most likely have the seasonal flu. It's important to limit your contact with others to keep from infecting them. Limitation: False positives (when your test says you have the flu, but you really don't) are very uncommon. Next step: Most people who have the flu won't need antiviral medicine to get better, but your provider may prescribe it depending on your health and how long you've been sick.
- Negative: A negative result means you may not have the flu. A different virus or bacteria may be causing your symptoms. Limitation: But the flu can't be ruled out. That's because your results could be a false negative (when your test says you don't have the flu, but you really do.) Next step: If you have negative test results and flu-like symptoms, ask your provider what you should do next.
- False negatives are possible, especially with rapid antigen tests or if the sample is collected when the virus level is low.
- False positives are very uncommon but can occur.
What to do next
To help ease your symptoms, get plenty of rest and drink lots of liquids. But children and teens should never take aspirin for flu-like symptoms. That's because aspirin increases the risk of Reye Syndrome, a rare, but serious illness that can happen after a viral illness.
- Do you have symptoms of a respiratory infection such as fever, chills, muscle aches, fatigue, headache, runny or stuffy nose, sore throat, or cough?
- Are you at high risk for serious flu complications (e.g., age under 5, age 65+, or chronic conditions like asthma, diabetes, heart disease)?
- Have you been in contact with animals that could have had bird flu (e.g., birds or cows) and have flu symptoms?
Evidence source
Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.