When you develop a fever and visit a hospital, the influenza testing performed will primarily involve two types: the “Rapid Antigen Test” and the “PCR Test (Genetic Test).”
The Rapid Antigen Test is appealing for its convenience, offering results in 15 minutes, but it carries the risk of false negatives. This accuracy can plummet to below 50% after 48 hours post-onset. In contrast, the PCR test boasts nearly perfect accuracy, ranging from 99.5% to 100%, but it comes with the drawbacks of time and cost.
Influenza “PCR vs. Rapid Antigen Test” Thorough Comparison (2025 Japan)
| Item | Rapid Antigen Test (15-Minute Nasal Swab) | PCR Test (Genetic Test) |
| Time to Result | 5–15 minutes (On the spot) | 40 minutes – Next day (Varies by hospital) |
| Accuracy (Sensitivity) | Type A: 88–95% | Type B: 70–85% |
| False Negative Rate (12–36 hours) | Type A: 5–10% | Type B: 15–25% |
| False Negative Rate (48+ hours) | 50–90% | Nearly 0% (Still detectable even after 72 hours) |
| Cost (30% Co-pay) | ¥600–¥1,500 | ¥1,800–¥3,500 |
| Insurance Coverage Hurdle | Almost 100% applicable to anyone | Only when a doctor deems it “necessary” |
| Discomfort of Sample Collection | Nose 2cm: ★★★★☆ | Throat: ★★★☆☆ |
| Simultaneous Testing | Flu + COVID + RSV is standard | Also possible (Nearly all kits are multi-target) |
| Actual Frequency of Use | 99% of people receive this first | Only 1–3% of people receive this |
| Doctor’s Trust Level | Type A positive → 100% trust | Negative → 50–80% trust |
| Medication Dispensation on Negative Result | Commonly prescribed if symptoms are strong | Rarely prescribed if negative |
Current Usage Scenarios in 2025
| Situation | Test Actually Used |
| Common cold symptoms + fever | → 100% Antigen Test |
| Antigen test negative but symptoms strongly suggest flu | → Another Antigen test the next day, or medication without a test if symptoms are severe |
| Elderly, underlying conditions, or difficulty breathing | → PCR from the start |
| Fourth day of high fever despite two negative antigen tests | → Switch to PCR |
| Need to know the exact strain type for school/facility | → PCR |
| Went to the emergency room with a fever at 9 PM | → Antigen Test (PCR results available the next morning) |
Summary (The Reality in 2025)
| What You Want to Know | The Correct Answer |
| “I want results fast, cheap, and reasonably accurate.” | → Antigen Test is sufficient. |
| “I absolutely cannot afford a mistake (hospitalization, high risk).” | → PCR is the only choice. |
| Those who think “Antigen Negative = Not the flu” | → This is completely wrong! (Doctors only half-trust the negative result.) |
Most people will finish with the Antigen Test. PCR is reserved for “those who absolutely must know 100%” and “high-risk individuals.”
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:
| Rank | Product Name (Manufacturer) | Targets Detected | Sensitivity (Detection Rate) (Estimate: 12-48h Post-Onset) | Result Time | Approximate Price (Per Test) | Suitability for Pregnant Women / Children | Key Features & Availability |
| 1 | Panbio COVID-19/Flu A&B | COVID + Flu A/B | COVID: Approx. 90% | Flu: Approx. 85% | 15 mins | ¥1,980 – ¥2,480 | ◎ (Shallow Nasal Swab) |
| 2 | クイックナビ-Flu+COVID | Same (COVID + Flu A/B) | COVID: 88% | Flu: 80–85% | 15–20 mins | ¥1,780 – ¥2,200 | ◎ (Designed for children’s use) |
| 3 | KBM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) |
