Key Takeaways
- Rapid antigen flu tests have only moderate sensitivity (50-70%), so a negative result does not rule out flu.[1]
- Molecular tests (RT-PCR and rapid molecular) are the gold standard, with 90-100% sensitivity.[2]
- Antigen tests are most accurate on day 1-2 of symptoms; testing too early or too late increases false negatives.[5]
- A positive antigen test is usually reliable, with roughly 90-95% specificity.[1]
- At-home combined flu and COVID tests are available but have the same antigen-test limitations.[2]
- Antiviral treatment should not be delayed while waiting for test results.[4]
Here is the single most useful thing to know about flu testing: a negative rapid test does not reliably rule out flu. Rapid antigen tests, the kind you get at a pharmacy or urgent care, miss a meaningful share of real flu infections. Understanding that one fact will help you interpret your result correctly, which is the whole point of this guide.
This page covers the different types of flu tests, how accurate each one is, when to test, what it costs, and how to get tested. It is the companion to our Flu Season guide and our Influenza and Common Cold guide, which cover symptoms and treatment.
Types of Flu Tests: Antigen vs Molecular
There are two broad families of flu tests, and they work differently.[2]
| Test type | What it detects | Sensitivity | Result time |
|---|---|---|---|
| Rapid antigen (RIDT) | Viral proteins | 50-70%[1] | 10-15 minutes |
| Rapid molecular | Viral genetic material | 90-95%[2] | 15-30 minutes |
| RT-PCR (lab) | Viral genetic material | >95%[2] | Hours to a few days |
Antigen tests look for pieces of the virus's proteins, which is fast but less sensitive. Molecular tests look for the virus's genetic material, which is more sensitive but takes longer. The difference in sensitivity is the single most important thing to understand about flu testing.
How Accurate Is the Flu Test?
The accuracy of a flu test depends almost entirely on which type you get. The chart below shows the sensitivity of each type, which is the test's ability to correctly detect flu when it is present:[1][2]
Specificity, the ability to correctly identify people who do not have flu, is high across the board. Rapid antigen tests have roughly 90-95% specificity, so a positive result is usually trustworthy. The weakness of antigen tests is not false positives; it is false negatives.[1]
Why a Negative Rapid Test Doesn't Rule Out Flu
This is the point worth internalizing. Because rapid antigen tests miss 30-50% of real flu cases, a negative result is common even when you actually have the flu. The CDC is explicit that false negatives are especially common during peak flu activity, when the chance that your symptoms are flu is highest.[1]
Timing also matters. Antigen tests are most accurate on day 1-2 of symptoms, when the virus is shedding at its peak. Testing in the first few hours, before viral load has built up, or several days in, after it has started falling, both increase the chance of a false negative.[5]
Influenza B is also harder for antigen tests to detect than influenza A, so a negative rapid test is less reassuring when influenza B is circulating.[1]
At-Home Flu Tests
Over-the-counter at-home flu tests are now widely available, and most of them combine flu A, flu B, and COVID-19 in a single swab. They are convenient, but they use antigen technology, which means they carry the same moderate sensitivity and the same false-negative risk as a clinic-based rapid antigen test.[2]
An at-home test is most useful when a quick answer helps you decide whether to isolate or seek care. If the result is negative but your symptoms strongly suggest flu, or you are at high risk of complications, a molecular test or a clinical evaluation is the more reliable path.
Flu and COVID Combined Tests
Because flu and COVID-19 cause nearly identical symptoms, a combined test that checks for both in one swab is often the most practical choice during respiratory season. Many at-home kits and clinic tests now test for flu A, flu B, and COVID-19 at once.[2]
The trade-off is the same: combined antigen tests are convenient but less sensitive than molecular tests. If the answer will change your treatment, such as whether to start an antiviral, a molecular test is more reliable.
Where to Get a Flu Test
Flu tests are available in several settings, each with different trade-offs in speed, cost, and accuracy:
| Setting | Typical test | Notes |
|---|---|---|
| Pharmacy | Rapid antigen, some rapid molecular | Fast and convenient; antigen tests have the false-negative caveat. |
| Urgent care | Rapid antigen or rapid molecular | Can also evaluate you clinically and prescribe if needed. |
| Doctor's office | Rapid molecular or RT-PCR | More likely to use a molecular test when accuracy matters. |
| Telehealth | Clinical diagnosis, can order a test | A video visit can diagnose flu and prescribe antivirals without an in-person swab. |
| At home | Combined antigen test | Convenient, but antigen sensitivity applies. |
How Long Does a Flu Test Take?
Result time depends on the test type, and it is the main reason antigen tests remain popular despite their lower accuracy:
If you need a fast answer to decide whether to isolate or start treatment, a rapid antigen or rapid molecular test makes sense. If accuracy matters more than speed, a laboratory RT-PCR is the reference standard.[2]
Flu Test Cost
Cost varies widely by setting and insurance. At-home combined flu and COVID tests typically run about $20 to $40 for a kit. Clinic and urgent-care tests are often covered by insurance; without insurance, a rapid test may cost roughly $50 to $100 or more depending on the facility and whether a clinician visit is billed separately.
If cost is a concern, a telehealth visit can be a lower-cost way to get a clinical diagnosis and, when appropriate, a prescription, without the separate charge for an in-person swab.
When Should You Get a Flu Test?
Not everyone with flu symptoms needs a test. Testing is most useful when the result will change what you do:[4][6]
| Situation | Should you test? |
|---|---|
| High risk of complications (65+, pregnant, chronic condition) | Yes, a confirmed diagnosis can prompt earlier antiviral treatment. |
| Need to distinguish flu from COVID-19 | Yes, a combined test clarifies treatment and isolation. |
| Live with someone at high risk | Worth testing to help protect them. |
| Mild illness, otherwise healthy adult | Optional; resting at home is reasonable. |
For a mild illness in an otherwise healthy adult, a test is often optional, and resting at home is reasonable. But do not let waiting for a test result delay treatment if you are high risk and within the 48-hour antiviral window.[4]
When to See a Doctor
Most flu can be managed at home, but seek care if you experience any of the following:[3]
- Difficulty breathing or shortness of breath
- Persistent chest pain or pressure
- Confusion or difficulty staying awake
- Severe or persistent vomiting
- Symptoms that improve, then return with fever and a worse cough
People at high risk of complications should contact a clinician early in the illness, because antivirals work best within the first 48 hours.[4]
Frequently Asked Questions
A flu test detects influenza virus in a respiratory sample, usually a nasal or throat swab. The two main types are rapid antigen tests and molecular tests (RT-PCR and rapid molecular), which differ in how accurate they are and how fast results come back.[2]
Yes, especially with rapid antigen tests. Because their sensitivity is only about 50% to 70%, false negatives are common, particularly during peak flu activity, very early in illness, and for influenza B. A negative rapid test does not rule out flu.[1]
A rapid antigen test detects viral proteins and gives results in 10 to 15 minutes but is less sensitive. PCR detects viral genetic material, is far more accurate, and takes longer (hours to days, or 15 to 30 minutes for rapid molecular tests).[2]
Yes. Over-the-counter at-home tests, most of which combine flu and COVID-19, are available. They use antigen technology, so they have the same moderate sensitivity and the same risk of false negatives as clinic-based rapid antigen tests.[2]
Rapid antigen tests give results in about 10 to 15 minutes. Rapid molecular tests take about 15 to 30 minutes. Laboratory RT-PCR can take several hours to a few days depending on the lab.[2]
Cost varies by setting. At-home combined flu and COVID tests typically run about $20 to $40. Clinic and urgent-care tests may be covered by insurance; without insurance, a rapid test may cost roughly $50 to $100 or more depending on the setting.
Testing is most useful when the result will change care, such as during flu season if you are at high risk of complications, if you need to confirm a diagnosis, or if distinguishing flu from COVID-19 matters for treatment or isolation.[4]
Not necessarily. Antiviral treatment should not be delayed while waiting for test results, and clinicians can prescribe based on symptoms and local flu activity, especially for high-risk patients within the 48-hour window.[4]
Yes, if it is a combined test. Many at-home and clinic tests now check for flu A, flu B, and COVID-19 in a single swab. A flu-only test cannot distinguish flu from COVID-19.[2]
Rapid antigen tests have the same moderate sensitivity in children as in adults, and influenza B in particular can be missed. Molecular tests are more accurate and are preferred when the result will change management.[1]
Flu tests are available at pharmacies, urgent care centers, doctor's offices, and through telehealth, which can order a test or diagnose flu by video visit. At-home combined tests are available over the counter.
References
- Centers for Disease Control and Prevention (CDC). Information for Clinicians on Rapid Diagnostic Testing for Influenza. https://www.cdc.gov/flu/hcp/testing-methods/rapidclin.html
- Centers for Disease Control and Prevention (CDC). Overview of Influenza Testing Methods. https://www.cdc.gov/flu/hcp/testing-methods/index.html
- Centers for Disease Control and Prevention (CDC). Rapid Diagnostic Testing for Influenza: Information for Clinical Laboratory Directors. https://www.cdc.gov/flu/php/laboratories/rapidlab.html
- Uyeki TM, Bernstein HH, Bradley JS, et al. Clinical Practice Guidelines by the Infectious Diseases Society of America: 2018 Update on Diagnosis, Treatment, Chemoprophylaxis, and Institutional Outbreak Management of Seasonal Influenza. Clin Infect Dis. 2019;68(6):e1-e47. doi:10.1093/cid/ciy866
- Tanei M, Yokokawa H, Murai K, et al. Factors influencing the diagnostic accuracy of the rapid influenza antigen detection test (RIADT): a cross-sectional study. BMJ Open. 2014;4(1):e003885. PMID 24384898
- Centers for Disease Control and Prevention (CDC). Diagnosing Flu. https://www.cdc.gov/flu/symptoms/testing.html