Table 6.
Influenza Diagnostic Tests for Respiratory Specimens
| Testing Category | Method | Influenza Viruses Detected | Distinguishes Influenza A Virus Subtypes | Time to Results | Performance |
|---|---|---|---|---|---|
| Rapid molecular assay | Nucleic acid amplification | Influenza A or B viral RNA | No | 15–30 minutes | High sensitivity; high specificity |
| Rapid influenza diagnostic test | Antigen detection | Influenza A or B virus antigens | No | 10–15 minutes | Low to moderate sensitivity (higher with analyzer device); high specificity; |
| Direct and indirect immunofluorescence assays | Antigen detection | Influenza A or B virus antigens | No | 1–4 hours | Moderate sensitivity; high specificity |
| Molecular assays (including RT-PCR) | Nucleic acid amplification | Influenza A or B viral RNA | Yes, if subtype primers are used | 1–8 hours | High sensitivity; high specificity |
| Multiplex molecular assays | Nucleic acid amplification | Influenza A or B viral RNA, other viral or bacterial targets (RNA or DNA) | Yes, if subtype primers are used | 1–2 hours | High sensitivity; high specificity |
| Rapid cell culture (shell vial and cell mixtures) | Virus isolation | Influenza A or B virus | Yes | 1–3 days | High sensitivity; high specificity |
| Viral culture (tissue cell culture) | Virus isolation | Influenza A or B virus | Yes | 3–10 days | High sensitivity; high specificity |
Negative results may not rule out influenza. Respiratory tract specimens should be collected as close to illness onset as possible for testing. Clinicians should consult the manufacturer’s package insert for the specific test for the approved respiratory specimen(s). Most US Food and Drug Administration (FDA)-cleared influenza diagnostic tests are approved for upper respiratory tract specimens but not for sputum or lower respiratory tract specimens. Specificities are generally high (>90%) for all tests compared to RT-PCR. FDA-cleared rapid influenza diagnostic tests are Clinical Laboratory Improvement Amendments (CLIA)-waived; most FDA-cleared rapid influenza molecular assays are CLIA-waived, depending on the specimen.
Abbreviation: RT-PCR, reverse-transcription polymerase chain reaction.