At-home COVID-19 tests, often called rapid antigen tests, let you check for an active infection in about 15 minutes using a simple nasal swab. They’re available over the counter at pharmacies, grocery stores, and online without a prescription. Here’s what you need to know to use one correctly and trust your results.
How At-Home COVID Tests Work
These tests use a technology called lateral flow immunoassay, which is a fancy way of saying the test strip catches virus proteins as your sample moves across it. When you swab your nose and mix the sample with the included liquid, that mixture travels along a small strip by capillary action, the same force that pulls water up a paper towel. If COVID proteins are present, they bind to antibodies on the strip and produce a visible colored line, typically using tiny gold or latex particles to create the color.
The specific protein these tests target is called the nucleocapsid protein, found inside the virus. This protein has stayed relatively stable even as the virus has mutated through different variants. That means current at-home tests still reliably detect newer strains of COVID-19.
How to Swab Correctly
The most common mistake people make is not swabbing deeply enough or rushing through it. For a standard anterior nasal swab (the type included with most home kits), insert the entire tip of the swab, usually about half to three-quarters of an inch, inside one nostril. Press the swab firmly against the inside wall of your nose and rotate it in a circular motion at least four times. Spend about 15 seconds per nostril. Most test instructions will have you repeat this in the other nostril using the same swab.
A gentle but firm touch matters. You’re not just tickling the inside of your nose. You need to collect enough cellular material from the nasal wall for the test to have something to work with. Follow the specific instructions in your kit, since some brands have slight variations in timing or the number of drops of liquid you add to the sample.
How Accurate Are These Tests?
At-home tests are very good at confirming infection when you have symptoms and a high viral load. In evaluations of five popular rapid tests (including BinaxNOW, iHealth, and QuickVue), all showed 100% sensitivity for samples with high viral loads. When the virus was present in large quantities, every test caught it every time.
The picture changes when viral load is low, which typically happens very early in infection, very late in infection, or in people without symptoms. At low viral loads, sensitivity dropped dramatically, ranging from about 4% to 46% depending on the brand. This is why a single negative result doesn’t guarantee you’re COVID-free.
The good news: specificity is excellent. Almost all major brands scored 100%, meaning false positives are extremely rare. If your test shows a positive result, you almost certainly have COVID.
Compared to PCR tests (the lab-based gold standard), home antigen tests are about 50% sensitive overall during the infectious period. But when compared against viral cultures, which measure whether someone is actually contagious, sensitivity jumps to 84%. In practical terms, these tests are better at telling you whether you’re contagious right now than whether traces of the virus are lingering in your system.
What a Faint Line Means
Any visible line in the test region, no matter how faint, counts as a positive result. The FDA is explicit about this: a faint colored test line alongside a visible control line should be read as positive. A faint line typically means there’s less viral protein in your sample, which could indicate you’re early or late in your infection. But it still means the virus was detected, and you should treat it the same as a bold, dark line.
If you see no test line at all, that’s a negative result. If neither line appears, including the control line, the test didn’t work properly and you should try again with a new kit.
When One Test Isn’t Enough
The FDA recommends repeat testing to increase confidence in a negative result. If you have symptoms and test negative, test again 48 hours later. Two negative antigen tests taken 48 hours apart give you much more confidence than a single negative. If you have no symptoms but want to rule out infection (after an exposure, for instance), you need three negative tests, each spaced 48 hours apart.
This serial testing approach compensates for the lower sensitivity of antigen tests at low viral loads. If you test too early after exposure, the virus may not have replicated enough to trigger a positive. Testing again two days later catches many of the infections that a first test misses.
Check the Expiration Date
Before using a test, check the expiration date on the box. Many at-home tests have had their shelf lives extended by the FDA after manufacturers submitted real-time stability data showing the tests remain accurate beyond their original printed dates. This means the expiration date printed on your box may no longer be correct.
To check whether your test has received an extension, visit the FDA’s “At-Home OTC COVID-19 Diagnostic Tests” page online. You can search by brand name and lot number. If your test has an extended date, it’s still safe and effective to use even if the box says otherwise. If you can’t find your test on the FDA site, you can also contact the manufacturer directly with the catalog number, lot number, and manufacturing date.
What to Do After Getting Your Result
If your test is positive, assume you have COVID-19. The CDC recommends staying home, isolating from others, and contacting a healthcare provider about next steps, including whether antiviral treatment makes sense for you. Starting treatment early (within the first few days of symptoms) is most effective, so don’t wait on this step.
You can also voluntarily report your result, positive or negative, through MakeMyTestCount.org or through a digital reporting option that may come with your kit. Home test results aren’t automatically captured by public health systems the way lab results are, so self-reporting helps health officials track how the virus is spreading in your community.
If your test is negative but you still feel sick, follow the serial testing schedule: test again in 48 hours. Many people who ultimately test positive get a negative result on their first try, especially in the first day or two of symptoms.
Do These Tests Still Work on Current Variants?
Yes. The nucleocapsid protein that home tests detect has remained relatively unchanged across the variants that have emerged so far. While the spike protein on the virus’s surface has mutated significantly (which is why vaccines need updating), the internal protein these tests target has stayed stable enough that existing test designs continue to work. Research confirms that antigen tests do a good job picking up a variety of COVID-19 variants, and infectious disease specialists say this pattern is expected to continue.