How many minutes after buffer extraction should rapid COVID/Flu antigen cassette test results be read?
Short answer
Rapid COVID-19 and flu antigen cassette test results should be read between 10 and 15 minutes after adding the extracted buffer drops to the sample well. Reading the test earlier than 10 minutes can cause false-negative results, while reading after 20 to 30 minutes produces false-positive evaporation lines. Setting a timer and checking the cassette strictly at the 15-minute mark ensures accurate and dependable results.
Rapid COVID-19 and Influenza antigen cassette tests should be read between 10 and 15 minutes after applying the extracted buffer sample, and never interpreted after 20 to 30 minutes.
During respiratory illness seasons, healthcare staff and caregivers rely on multiplex antigen cassettes (lateral flow diagnostic tests that detect COVID-19 and Flu A/B on a single strip) for point-of-care decisions. Standard laboratory protocols establish strict timing windows because capillary flow and antibody binding change optical visibility as the strip dries.
If you only do one thing: Set a digital timer immediately after adding the extracted buffer drops to the cassette well, and read the test window strictly at the 15-minute mark.
- Extraction swirling: Swirl the collected nasal swab in the extraction buffer vial for 15 to 30 seconds while pinching the tube walls to extract viral protein antigens.
- Sample dispensing: Apply the manufacturer-specified volume—typically 3 to 4 drops (approximately 100 microliters)—directly into the cassette sample well ("S").
- Membrane migration: Allow the liquid to migrate across the nitrocellulose strip via capillary action (liquid flow through absorbent test paper) on a flat, level surface at room temperature (59°F to 86°F or 15°C to 30°C).
- Primary interpretation window: Observe the control ("C") and test lines ("COVID-19", "Flu A", "Flu B") between 10 and 15 minutes, verifying that a visible control line confirms test validity.
- Disposal cut-off: Discard the used cassette after 20 to 30 minutes, as dried reagents and evaporation lines no longer reflect an active diagnostic reading.
- Watch out for: Reading results earlier than 10 minutes, which risks false-negative results before lower concentrations of viral antigens have completed binding to detection antibodies.
- Watch out for: Interpreting cassette lines after 30 minutes, where normal evaporation creates faint gray or ghost lines that mimic false-positive results.
- Watch out for: Moving or tilting the cassette during the 15-minute migration run, which causes irregular liquid flow and invalidates the control line.
Verify the exact timing instructions printed on your specific test kit package insert before opening the foil pouch. Consult a qualified medical provider to interpret symptoms or determine clinical treatment for acute respiratory illness.