A Rapid Antigen Test, or RAT, is a quick diagnostic tool designed to identify specific viral proteins called antigens. These tests offer a swift method for detecting active infections, such as those caused by SARS-CoV-2. They are used at the point of care, including self-testing at home, providing results within a short timeframe of 5 to 30 minutes. This makes them a convenient option for initial screening.
The Science Behind Rapid Antigen Tests
Rapid antigen tests operate on a lateral flow immunoassay. This technology utilizes a small strip with distinct pads and a nitrocellulose membrane. When a liquid sample is applied to the sample pad, it begins to move along the strip through capillary action.
The sample first reaches a conjugate pad containing detector particles that are coated with specific antibodies. These antibodies bind precisely to target viral antigens. If present, they attach to these antibody-coated particles.
This antigen-antibody complex then continues to flow along the membrane until it reaches a test line, which has immobilized antibodies. These immobilized antibodies capture the complex, forming a visible line, indicating a positive result. A separate control line also appears, confirming that the test functioned correctly.
How to Correctly Perform a Test
Before beginning a rapid antigen test, wash your hands with soap and water and ensure all kit components are at room temperature, as cold reagents can affect accuracy. Read the instructions provided with your test kit, as procedures can vary between brands regarding sample collection, number of drops, and reading time.
For nasal swab collection, gently blow your nose to clear any mucus, aiming to sample the tissue lining the nasal passages, not just the inside of the nostril. Insert the swab horizontally, rather than straight up, approximately 2-3 centimeters into one nostril, then rotate it gently against the walls for the recommended number of rotations (typically five to ten). Repeat this process in the second nostril using the same swab. Avoid touching the swab tip with your fingers or other surfaces, as this can contaminate the sample and lead to inaccurate results.
Once the sample is collected, immediately place the swab into the extraction buffer solution, swirling and squeezing the swab against the tube’s sides to release material. Then, dispense the specified number of drops onto the designated sample well on the test cassette. Set a timer for the duration indicated in the instructions (usually 10-30 minutes), and read the result only within this timeframe, as readings outside it may be unreliable.
Understanding Your Results and Next Steps
Interpreting results involves looking for colored lines on the test cassette. A positive result is indicated by the appearance of two distinct lines: one at the control (C) region and another at the test (T) region, regardless of how faint the test line appears. A positive result means SARS-CoV-2 antigens were detected, suggesting an active infection. Isolate yourself and follow local public health guidelines.
A negative result shows only one colored line at the control (C) region, with no line appearing at the test (T) region. This indicates no target antigens were detected above its detection threshold. A negative result does not completely rule out an infection, especially if you were tested very early in the infection, have a low viral load, or were exposed to the virus recently. If you have symptoms or recent exposure, it is advisable to retest after a few days or seek further medical advice.
An invalid result occurs if no line appears at the control (C) region, or if lines appear erratically, indicating the test did not function properly. This can happen due to incorrect sample collection, improper test execution, or a faulty test kit. If your test yields an invalid result, discard the kit and perform a new test using a fresh kit.