Influenza Test Accuracy: “Trust Type A, Be Skeptical of Type B” – A Doctor Reveals the Limits and Accuracy of the Rapid Influenza Test
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Do you know how much a doctor actually relies on the result of a rapid test kit when diagnosing the flu? Many of the rapid antigen test kits used during the 2024-2025 season boast a sensitivity close to 90% for Type A influenza, but their sensitivity for Type B influenza tends to be lower, around 60% to 80%. This difference becomes a major issue, especially during the peak season.
Summary of Rapid Influenza Antigen Test Accuracy (2024-2025 Season)
Testing Method
Sensitivity (Probability of correctly identifying a positive person)
Specificity (Probability of correctly identifying a negative person)
Perceived Accuracy in Practice
Common Rapid Antigen Kit(Most used in medical settings)
Type A: 80–90%
Type B: 60–80%
95–99%
Peak Sensitivity (12–24 hours post-onset)
Type A: 90–95%
Type B: 75–85%
Nearly 100%
48+ Hours Post-Onset
Type A: 50–70%
Type B: 40–60% or lower
Nearly 100%
The Three Major Factors Affecting Accuracy
Factor
Impact
Specific Example
① Time Elapsed Since Onset
Most Important!!
Peak is 12–24 hours → Too early or too late causes a significant drop.
② Virus Type
Type B inherently has low sensitivity.
If Type B (Victoria lineage) is prevalent in the 2024-25 season, false negatives will be frequent.
③ Specimen Collection
Failure to collect properly from deep in the nose causes false negatives.
Particularly difficult for children or those with nasal congestion.
Common Scenarios in the Clinical Setting
Situation
Test Result
What is the Reality?
15 hours post-onset, high fever + joint pain
Positive
Almost 100% genuine.
15 hours post-onset, typical symptoms
Negative
20–30% is a false negative (especially Type B).
60 hours post-onset, still 38°C
Negative
70–80% is a false negative (viral load has sharply decreased).
Negative result, re-tested the next day
Positive
Extremely common (“It was too early yesterday” pattern).
A Doctor’s Honest View on Accuracy
“If it’s Type A, I mostly trust the rapid test.”
“If it’s Type B and negative, I’m still skeptical (especially during peak season).”
“If it’s negative after 48 hours, I assume it’s probably not the flu.”
Summary
Within 12–36 hours post-onset + Type A prevalent season → Rapid test accuracy is over 90% and reliable.
Other cases (especially Type B, too early, or too late) → Assume that 30–40% of negative results could be false negatives.
At-Home Testing Kit Ranking (Combined COVID-19 and Influenza)
Here is the English translation of the ranking table for at-home diagnostic kits that test for both COVID-19 and Influenza A/B:
