Can Other Antigens Cause False-Positive Rapid Influenza Tests?
No, other respiratory viral antigens such as RSV, adenovirus, or coronavirus do not typically cause false-positive results on rapid influenza tests—these tests have high specificity (>90-95%) for influenza antigens. 1, 2, 3
Understanding Rapid Influenza Test Specificity
The primary limitation of rapid influenza diagnostic tests (RIDTs) is their low sensitivity (10-70%), not their specificity. 1, 2, 3 This means:
- False-negative results are common (missing true influenza infections) 1
- False-positive results are rare when tests are functioning properly 1, 3
- Specificity consistently exceeds 90-95% across different RIDT platforms 1, 2, 3
What Actually Causes False-Positive Rapid Influenza Tests
While cross-reactivity with other respiratory viruses is not a significant concern, false-positive results can occur due to:
Test-Related Issues
- Test kit malfunction or manufacturing defects, which should be suspected when results don't match clinical presentation 4
- Improper test performance or interpretation by the operator 1
- Low community influenza prevalence, which dramatically reduces positive predictive value even with high specificity 1, 3
Specimen Contamination
- Influenza vaccine contamination at the collection site—vaccine RNA can be detected for at least 66 days after administration and can contaminate specimens collected in the same location where vaccines are given 5
- Laboratory cross-contamination between specimens, though this is less common with point-of-care rapid tests 5
Post-Vaccination Detection
- Recent live attenuated influenza vaccine (LAIV) can cause positive tests up to 7 days after administration, representing vaccine virus detection rather than true infection 1
Clinical Approach When Results Don't Match Clinical Picture
When a positive rapid test doesn't fit the clinical scenario:
- Check if the patient received influenza vaccine recently (within 7 days for LAIV, or if specimen was collected at a vaccination site) 1, 5
- Assess local influenza activity—during low prevalence periods, positive predictive value drops substantially 1, 3
- Consider confirmatory RT-PCR testing, which has 86-100% sensitivity and high specificity 2, 6, 3
- Trust the PCR result over the rapid test if discordant 3
Important Caveats
The differential diagnosis should still include other respiratory pathogens that can present identically to influenza, including RSV, parainfluenza viruses, adenovirus, human metapneumovirus, coronaviruses, Mycoplasma pneumoniae, and Streptococcus pneumoniae. 1, 6 However, these pathogens cause false-negative rapid influenza tests (by causing influenza-like illness without influenza), not false-positive results. 7
During influenza season with high community activity, positive rapid tests are generally reliable and should guide treatment decisions. 1 The concern about false-positives primarily applies to periods of low influenza circulation. 3