Influenza Diagnosis in Clinical Practice: Comparing Rapid Antigen Tests and RT-PCR with Age-Stratified Results

Abstract

Aim: To evaluate the diagnostic sensitivity of a commercially available rapid influenza antigen test in comparison to reverse-transcription polymerase chain reaction (RT– PCR), and to examine the impact of age on test performance. Material and Methods: We conducted a single-center, retrospective diagnostic sensitivity study at Kafkas University Faculty of Medicine Hospital between January and April 2025. Consecutive symptomatic patients were tested using multiplex RT-PCR on nasopharyngeal swabs. The index test (SD Bioline Influenza A/B RADT) was only performed on RT-PCR-positive samples following the manufacturer’s instructions. The primary endpoint was the sensitivity of the SD Bioline Influenza A/B RADT for influenza A and B overall and by age group (pediatric <18 years, adult ≥18 years). We also documented cases where RT-PCR-confirmed influenza A samples produced influenza B readings on the RADT and compared their frequency by age group. Statistics: sensitivity and 95% confidence intervals (CIs) were calculated using the Wilson method; subgroup comparisons employed Fisher’s exact test. As per the study design, specificity, positive predictive value (PPV), and negative predictive value (NPV) could not be estimated. Results: Out of 531 symptomatic cases, 92 tested positive via RTPCR (influenza A: 78; influenza B: 14). The RADT exhibited an overall sensitivity of 81. 5%, with subtype-specific sensitivities of 78. 2% for influenza A and 100% for influenza B. Sensitivity was higher in children than in adults (92. 9% vs. 74. 0%, p=0. 03). A small subset of RT-PCR-confirmed influenza A samples produced influenza B readings on the RADT; none of these were RT-PCR-positive for influenza B. Specifically, in 11 of 78 RT-PCR-confirmed influenza A samples (14. 1%; 95% CI 8. 8.1–23. 5), the RADT read influenza B; none of these 11 samples were RT-PCR-positive for influenza B. Conclusion: Rapid antigen tests are reliable tools for diagnosing influenza in children, given their higher sensitivity in this group. However, in adults, the lower sensitivity means that negative results should be interpreted with caution and may require confirmation by RT-PCR.

Keywords

• influenza virus
• RT-PCR diagnosis
• rapid antigen test
• age-related diagnostic performance; age-dependent immune response

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