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Rapid Diagnostic Testing for Influenza: Information for Health Care Professionals

Background

Rapid diagnostic tests for influenza can help in the diagnosis and management of patients who present with signs and symptoms compatible with influenza. They also are useful for helping to determine whether outbreaks of respiratory disease, such as in nursing homes and other settings, might be due to influenza.

Reliability and Interpretation of Rapid Test Results

Proper interpretation of test results is very important for accurate clinical management of patients with suspected influenza. The reliability of rapid diagnostic tests depends largely on the conditions under which they are used. Understanding some basic considerations can minimize being misled by false-positive or false-negative results.

  • Sensitivities of rapid influenza diagnostic tests are approximately 50-70%, and specificities of rapid diagnostic tests for influenza are approximately 90-95%, when compared with viral culture or reverse transcription polymerase chain reaction (RT-PCR)
  • False-positive (and true-negative) results are more likely to occur when disease prevalence in the community is low, which is generally at the beginning and end of the influenza season.
  • False-negative (and true-positive) results are more likely to occur when disease prevalence is high in the community, which is typically at the height of the influenza season.

Minimize False Results

  • Use rapid diagnostic tests with high sensitivity and specificity.
  • Collect respiratory tract specimens as early in the illness as possible, (within 3-4 days of illness onset).
  • Follow manufacturer’s instructions, including handling of respiratory specimens, as described in the device package insert.
  • Consider sending respiratory specimens for RT-PCR to confirm results of rapid tests especially when community influenza activity is low and the rapid diagnostic test result is positive and when the rapid diagnostic test result is negative but influenza activity is high. (Contact your local or state health department for information about influenza activity).

 

Table: Influenza Virus Testing Methods
Method1 Types Detected Acceptable Specimens2 Test Time CLIA Waived3
Viral tissue cell culture (conventional; yields live virus) A and B NP4 swab, throat swab, NP2 or bronchial wash, nasal or endotracheal aspirate, sputum 3-10 days No
Rapid cell culture (shell vials; cell mixtures; yields live virus) A and B As above 1-3 days No
Immunofluorescence, Direct (DFA) or Indirect (IFA) Florescent Antibody Staining [antigen detection] A and B NP4 swab or wash, bronchial wash, nasal or endotracheal aspirate 1-4 hours No
RT-PCR5 (singleplex and multiplex; real-time and other RNA-based) and other molecular assays [influenza viral RNA or nucleic acid detection] A and B NP4 swab, throat swab, NP2 or bronchial wash, nasal or endotracheal aspirate, sputum Varies by assay (Generally 60-80 minutes and 4-8 hours) No
Rapid Molecular Assay [influenza viral RNA or nucleic acid detection] A and B NP4 swab, nasal aspirate, wash, swab Approximately 20 minutes7 Yes/No7
Rapid Influenza Diagnostic Tests6 (antigen detection) A and B NP4 swab, (throat swab), nasal wash, nasal aspirate <15 min. Yes/No
  1. Serologic (antibody detection) testing is not recommended for routine patient diagnosis.
  2. Ref: Leland, et al. 2007, Clin Micro Rev 20: 49-78. Approved respiratory specimens vary among FDA cleared influenza assays.
  3. Ref: http://www.cms.gov/Regulations-and-Guidance/Legislation/CLIA/index.html
  4. NP = nasopharyngeal
  5. Reverse transcription polymerase chain reaction, including FDA-approved test systems, reference laboratory testing using ASR or lab-developed reagents
  6. Chromatographic- and/or fluorescence-based lateral flow and membrane-based immunoassays
  7. Rapid molecular assays can provide results in approximately  20 minutes. Alere i Influenza A&B was FDA cleared for use with both nasal swabs (direct) and NP or nasal swabs in VTM. It was CLIA-waived for use with nasal swabs (direct) only. Roche Cobas Influenza A/B was cleared and CLIA-waived by FDA for use with nasopharyngeal swabs only.
  8. VTM = Viral transport media
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Table: Characteristics of Rapid Influenza Diagnostic Tests (Antigen Detection Only)1
Procedure
(Manufacturer/Distributor)
Influenza Virus
Types Detected
Approved Specimens2 CLIA Waived3 Uses Analyzer Reader Device
BD Directigen™ EZ Flu A+B4
(Becton-Dickinson & Co.)
A and B NP5 wash/aspirate/swab
Throat swab
No No
BD Veritor™ System for Rapid Detection of Flu A+B4 (CLIA-waived),
(Becton Dickinson & Co.)
A and B NP5 swab/
nasal swab
Yes Yes
BD Veritor™ System for Rapid Detection of Flu A+B4 (Moderately Complex), (Becton Dickinson & Co.) A and B NP5 wash/aspirate No Yes
Binax NOW® Influenza A&B4 Test
(Alere Scarborough, Inc.)
A and B NP5 swab,
Nasal wash/aspirate/swab
Yes No
BioSign® Flu A+B4
or
OraSure QuickFlu Rapid A+B Test
or
Polymedco Poly stat Flu A&B Test
or
LifeSign LLC Status Flu A&B (Princeton BioMedtech Corp.)
A and B NP5 swab/aspirate/wash, nasal swab No No
ClearView Exact II Influenza A&B Test or
Alere Influenza A&B Test
(Alere Scarborough, Inc.)
A and B Nasal swab Yes No
OSOM® Influenza A&B4 Test
(Sekisui Diagnostics)
A and B Nasal swab No No
QuickVue® Influenza A/B Test6
(Quidel Corp.)
A and B Nasal wash/aspirate/swab Yes No
QuickVue® Influenza A+B Test4
(Quidel Corp.)
A and B NP5 swab
Nasal wash/aspirate/swab
Yes No
RAMP Influenza A/B Assay
or
3M™ Rapid Detection Flu A+B Test4
(Response Biomedical Corp.)
 
A and B NP5 swab/aspirate
Nasal wash/aspirate
No Yes
SAS™ FluAlert A&B Test4
(SA Scientific, Inc.)
A and B Nasal wash/aspirate No No
SAS™ Influenza A Test4
(SA Scientific, Inc.)
A only Nasal wash/aspirate Yes No
SAS™ Influenza B Test4,6
(SA Scientific, Inc.)
B only Nasal wash/aspirate Yes No
Sofia® Analyzer and Influenza A+B FIA4
(CLIA-waived) (Quidel Corp.)
A and B NP5 swab
Nasal swab
Yes Yes
Sofia® Analyzer and Influenza A+B FIA4
(Quidel Corp.)
A and B NP5 aspirate/ wash No Yes
TRU FLU®4
(Meridian Bioscience, Inc.)
A and B NP5 aspirate/swab
Nasal wash/swab
No No
XPECT™ Influenza A/B4
(Remel Inc./Thermo Fisher Scientific)
A and B Nasal wash/swab
Throat swab
No No

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  1. List may not include all test kits approved by the U.S. Food and Drug Administration. Discontinued tests not included.
  2. Approved respiratory specimens according to manufacturer's package insert. Note that test performance may vary if other respiratory specimens are used.
  3. Ref: http://www.cms.gov/Regulations-and-Guidance/Legislation/CLIA/index.html
  4. Distinguishes between influenza A and B virus infections.
  5. NP = nasopharyngeal.
  6. Does not distinguish between influenza A and B virus infections when used alone.

Disclaimer: Use of trade names or commercial sources is for identification only and does not imply endorsement by the Centers for Disease Control and Prevention or the Department of Health and Human Services.

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