Rapid flu tests work much like the COVID-19 home tests you may already be familiar with: you swab your nose, mix the sample with a liquid solution, and read the results on a small test card in about 15 minutes. Most home flu tests available now are combination kits that check for COVID-19, influenza A, and influenza B all at once. Here’s how to do one correctly and what the results mean.
What You Need Before You Start
A typical home flu test kit contains a sealed test card (or cassette), a sterile nasal swab, a small vial of extraction buffer (the liquid solution), and a dropper or nozzle tip. Some kits include two tests per box, with each test individually packaged. Kits generally cost around $9 to $15 for a two-pack at pharmacies and online retailers.
Before opening anything, check the expiration date on the box. Store kits between 36°F and 86°F in their original packaging, away from direct sunlight, and never freeze them. If the kit has been sitting in a hot car or cold garage, bring it to room temperature (65°F to 86°F) before use. Once you open the sealed foil pouch containing the test card, you have about 60 minutes to use it. After that, results may not be accurate.
When to Test for the Best Results
Timing matters more than most people realize. Rapid flu tests detect pieces of the actual virus (viral antigens) in your nasal passages, and the amount of virus peaks early in your illness. For the most reliable result, test within three to four days of your first symptoms. Testing on day one or two is ideal. If you wait too long, viral levels drop and the test is more likely to miss an active infection.
Step-by-Step Instructions
Wash your hands, then lay out your supplies on a clean, flat surface. The exact steps vary slightly by brand, so always read the instructions in your specific kit. That said, nearly all home flu tests follow the same general process:
- Prepare the extraction buffer. Open the small vial of liquid that comes with the kit. Some kits require you to snap off the tip; others have a peel-off seal. Set the vial upright in the provided holder or cardboard stand so it doesn’t tip over.
- Collect your sample. Remove the sterile swab from its wrapper, tilt your head back slightly, and insert the soft tip about 1 to 1.5 inches (roughly 2 to 3 centimeters) into one nostril. Rotate the swab gently against the inside wall of your nostril five to ten times (your instructions will specify the exact count). Repeat in the other nostril with the same swab. The swab should feel slightly uncomfortable but not painful. If it doesn’t feel like anything, you probably haven’t inserted it far enough.
- Mix the swab in the buffer. Place the swab tip into the vial of liquid and stir or rotate it as directed, usually around 10 to 15 times. Then squeeze the sides of the vial against the swab as you pull it out. This transfers the sample from the swab into the liquid. Discard the swab.
- Apply the sample to the test card. Remove the test card from its foil pouch. Using the vial’s dropper tip, squeeze the specified number of drops (typically two to four) into the sample well on the card. Avoid touching the dropper to the card surface.
- Wait the full time. Set a timer for 15 minutes. Read results at the time your instructions specify. Reading too early can give incomplete results, and waiting too long (past 30 minutes for most kits) can cause faint lines to appear that aren’t true positives.
Reading Your Results
Most combination test cards have a small results window with labeled lines. You’ll typically see a control line (marked “C”) and separate test lines for COVID-19, Flu A, and Flu B. The control line must appear for the test to be valid. If it doesn’t show up, the test failed and you need to use a new one.
A colored line next to “Flu A” means influenza A is detected. A line next to “Flu B” means influenza B. Even a faint line counts as a positive result. If only the control line appears with no other lines, the test is negative for all targets it checks. It’s possible to test positive for more than one virus at the same time, though it’s uncommon.
Influenza A and B are different strains of the flu virus. Influenza A is more common and tends to cause more severe seasonal outbreaks. Influenza B typically produces milder illness but can still be serious. Knowing which type you have can help your doctor decide on treatment if you call about antiviral options, since treatment works best when started within 48 hours of symptoms.
How Accurate Are Home Flu Tests?
Rapid flu tests are much better at confirming a positive than ruling out a negative. A large meta-analysis comparing rapid antigen tests against the gold-standard PCR method found that these tests correctly identify about 61% of true flu infections (sensitivity) but are correct about 99% of the time when they say you don’t have the flu (specificity). In practical terms, if your rapid test says positive, it’s almost certainly right. But if it says negative and you still feel terrible, there’s a real chance you have the flu and the test missed it.
Several things can cause a false negative. Testing too late in your illness is the most common culprit. Not swabbing deeply enough or not rotating the swab long enough also reduces the amount of virus on the sample. Using a kit that’s been improperly stored, expired, or left open too long before testing can degrade the reagents. If you get a negative result but your symptoms strongly suggest the flu (sudden high fever, body aches, chills, extreme fatigue), consider retesting in 24 hours or contacting your healthcare provider about a more sensitive PCR-based test.
Tips to Avoid Common Mistakes
The single biggest error is a poor swab. People tend to barely insert the swab or rush through the rotation. Go slow, count your rotations, and make sure the swab tip actually contacts the inner wall of both nostrils. It should feel mildly uncomfortable.
Other common pitfalls: using too many or too few drops of buffer on the test card, not mixing the swab in the liquid long enough, and reading results outside the specified time window. Follow the drop count exactly. If your kit says three drops, don’t squeeze four because the vial still has liquid left. The leftover liquid is there by design to account for manufacturing tolerances.
Blow your nose gently before testing if you’re extremely congested, but don’t use nasal spray or rinse your sinuses right before swabbing. These can wash away the viral material the test needs to detect.
What’s Available for Home Use
The FDA granted full marketing authorization to the Healgen Rapid Check COVID-19/Flu A&B Antigen Test as the first over-the-counter combination flu and COVID test cleared through a traditional (non-emergency) review pathway. Several other combination tests are available under emergency use authorizations. You can find these at major pharmacies, grocery stores, and online. Most are nasal swab tests with 15-minute results and cost under $15 for a two-test box.
Standalone flu-only home tests also exist, though combination tests have become more popular since they screen for multiple viruses at once using a single swab. If you’re only concerned about influenza and not COVID-19, either type works, but the combination tests offer more information for the same effort.