Rapid COVID-19 tests, also known as rapid antigen tests or lateral flow tests, detect the SARS-CoV-2 virus, which causes COVID-19. They provide timely information, often within minutes, aiding personal health decisions and public health efforts to mitigate viral spread. Their ease of use makes them suitable for self-testing at home, increasing accessibility.
Understanding Rapid COVID Tests
Rapid COVID-19 tests detect specific viral proteins, known as antigens, from the SARS-CoV-2 virus. They use lateral flow immunoassay technology, with a test strip containing antibodies designed to bind to these antigens. When a sample containing viral antigens is applied to the test, the antigens bind to labeled antibodies and then to fixed antibodies on an indicator line, resulting in a visible colored line.
Sample collection most commonly involves a nasal swab, inserted into the nostrils to gather secretions. The sample is then mixed with a solution that releases viral proteins. This liquid sample is applied to the test cartridge for detection. The nucleocapsid protein is a common target for these antigen tests, as it is abundant during infection.
How to Use and Interpret Rapid Test Results
Before beginning a rapid COVID-19 test, carefully read the manufacturer’s instructions included in the kit, as specific steps can vary between brands. Start by washing your hands thoroughly with soap and water and ensure your testing area is clean and flat. Open the test kit components and place them on the clean surface, checking the expiration date to confirm the test is still valid.
For sample collection, gently insert the provided swab into one nostril, rotating it against the inner wall for at least 15 seconds. Repeat this process in the other nostril. After swabbing, place the swab into the extraction tube containing the liquid, stirring for at least 15 seconds while squeezing the tube as you remove it.
Attach the dropper tip to the collection tube and squeeze the specified number of drops, usually three, into the sample well on the test cassette. Set a timer for the duration specified in the instructions, typically 10 to 30 minutes, and avoid disturbing the test. Once the timer is complete, read the result:
- A line next to “C” (Control) indicates the test worked correctly.
- If a second line appears next to “T” (Test), regardless of how faint, the result is positive, meaning viral antigens were detected and you likely have COVID-19.
- If only the “C” line appears, the result is negative, indicating the virus was not detected at the test’s threshold.
- If no line appears, or only the “T” line appears, the test is invalid and needs to be repeated with a new kit.
If positive, isolate from others for at least 5 days (3 days for those under 18) to prevent spread. Monitor symptoms and avoid contact with high-risk individuals for 10 days. If symptoms worsen or you have underlying health conditions, contact a healthcare provider for guidance. A negative result suggests you are unlikely to have COVID-19, but it does not rule out infection, especially early on or if symptoms persist. If symptoms persist, repeat the test after 48 hours, or perform three tests over five days if asymptomatic.
Accuracy and Appropriate Use
Rapid COVID-19 test accuracy is described by sensitivity and specificity. Sensitivity is the test’s ability to correctly identify infected individuals (positive result). Specificity measures the test’s ability to correctly identify uninfected individuals (negative result). Rapid antigen tests have high specificity (98-99%), meaning false positives are rare. However, their sensitivity varies, averaging 69-75% compared to PCR tests.
Accuracy can be influenced by several factors. Viral load, the amount of virus in the body, is a significant factor; tests are more accurate when viral load is high, typically during peak infection a few days after exposure or symptom onset. Testing too early in an infection, when viral load is low, can lead to a false negative result. Proper sample collection technique is also important; mistakes can result in inaccurate outcomes.
Rapid tests are most effective in specific situations. They are more accurate for symptomatic individuals, especially within the first seven days of symptom onset. They are also useful for quick screening before gatherings, particularly when interacting with immunocompromised individuals, or for serial testing to increase detection likelihood. If exposed to COVID-19 but asymptomatic, wait at least five days after exposure before testing.
Rapid Tests Versus PCR Tests
Rapid antigen tests and PCR (polymerase chain reaction) tests are distinct approaches to diagnosing COVID-19, differing in detection method, speed, cost, and use. Antigen tests detect specific viral proteins, providing quick results, usually within 15 to 30 minutes. They are more affordable ($10-$200) and widely accessible for at-home use.
In contrast, PCR tests detect the genetic material (RNA) of the SARS-CoV-2 virus. This method amplifies tiny segments of viral genetic material, making PCR tests highly sensitive and capable of detecting the virus even at very low levels. While PCR tests are considered the gold standard for accuracy and can detect infection earlier than antigen tests, they require laboratory processing, with results typically taking 24 to 72 hours. Costs for PCR tests range from $25 to $300.
Each test type is preferred in different situations. Rapid antigen tests are suitable for quick screenings, especially when immediate results are needed for decisions about isolation or activities. PCR tests are recommended for confirming a COVID-19 diagnosis, particularly when high accuracy is needed, such as for symptomatic individuals with negative rapid test results, or for specific requirements like travel or healthcare clearance.