Influenza Antigen Test: The Complete Guide – It Only Takes 15 Minutes! When is it Accurate?

When you go to the hospital with a fever, the test you will almost certainly receive is the “Rapid Antigen Test (the 15-Minute Test).” This inexpensive and fast-acting test remains at the forefront of influenza diagnosis as of 2025.

However, behind its convenience lies a limitation: the possibility of a “false negative” (being negative when you actually have the virus). Its accuracy significantly decreases, especially for Type B influenza and when the test is performed more than 48 hours after the onset of symptoms.

Complete Summary of the Influenza “Antigen Test” (2025 Japan)

ItemDetails (2025 Latest Information)
Formal NameInfluenza Antigen Rapid Diagnostic Kit using the Immunochromatography Method
Common Names“Nasal Swab Test,” “15-Minute Test,” “Flu Test”
Time to Result5–15 minutes (Many latest kits take 5–8 minutes)
Specimen Collection SiteNasal cavity (2–3 cm inside the nose) or Pharynx (back of the throat)
2025 Mainstream KitsQuick Navi-Flu2 (Denka), Espline (Fujirebio), ImmunoAce Flu (Tauns), BD Veritor (Highest accuracy, higher cost)
Accuracy (Actual Values)Type A: 88–95%
Cost (30% Co-pay)¥600–¥1,500 (Varies by kit)
Insurance Coverage100% covered if the test is within 72 hours of onset AND deemed necessary by a physician.

Latest Trends as of 2025

ItemDetails
Simultaneous Test Kits are Nearly 100%Tests for Influenza A + B + COVID-19 + RSV in one go.
Kits with 5–8 Minute Results are MainstreamRapidly gaining popularity since 2024.
Type B Sensitivity Has Slightly ImprovedImproved from a conventional 65% to around 78–85%.
Nasal Swab is SufficientSensitivity is achieved even with a shallower swab than before.

Interpretation of Results

ResultDoctor’s Assessment
Type A Positive“100% trustworthy.”
Type B Positive“95% trustworthy.”
Type A Negative (12–36 hours)“90%+ trustworthy.”
Type B Negative (12–36 hours)“Skeptical” → Medication will be prescribed if symptoms are strong.
Both Negative (Over 48 hours)“Almost untrustworthy” → Decision based on symptoms.
Both Negative (Under 12 hours)“Just too early” → Instructed to retest tomorrow.

Summary

  • This is the test 99% of people receive first.
  • It’s over quickly (15 minutes), inexpensive, and reasonably accurate → This is why everyone uses it.
  • All doctors know that a negative result often means “bad timing.”
  • Therefore, if symptoms are typical, doctors will prescribe medication even with a negative result (especially during peak season).
  • “The Antigen Test = A convenient test that is 80–90% accurate in 15 minutes.”

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:

RankProduct Name (Manufacturer)Targets DetectedSensitivity (Detection Rate) (Estimate: 12-48h Post-Onset)Result TimeApproximate Price (Per Test)Suitability for Pregnant Women / ChildrenKey Features & Availability
1Panbio COVID-19/Flu A&B COVID + Flu A/BCOVID: Approx. 90%Flu: Approx. 85%15 mins¥1,980 – ¥2,480◎ (Shallow Nasal Swab)
2クイックナビ-Flu+COVIDSame (COVID + Flu A/B)COVID: 88%Flu: 80–85%15–20 mins¥1,780 – ¥2,200◎ (Designed for children’s use)
3KBMラインチェック nCoV/Flu Same (COVID + Flu A/B)COVID: 85%Flu: Approx. 80%15 mins¥1,480 – ¥1,980◎
4イージードック Flu＆COVID-19 Same (COVID + Flu A/B)COVID: 87%Flu: 82%15 mins¥2,200 – ¥2,600◎ (Many cases of use by pregnant women)