Diagnostic Influenza Tests 

Updated: Mar 28, 2014
  • Author: Elvia Martinez Blanco, MD; Chief Editor: Thomas M Wheeler, MD  more...
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Reference Range

Diagnostic influenza tests aid with identification of influenza types A and B and influenza A subtypes 2009 H1N1, H1, H3, H5, N1, and N2. Variation exists among diagnostic methods for identification of types and subtypes of influenza (see Tables 1, 2, and 3).

These tests can be used for any age or sex.

Qualitative: Positive or negative.

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Interpretation

If the value is positive, the patient may have influenza.

  • False-positive and true-negative test results occur more frequently when disease prevalence is low.

  • False-negative and true-positive test results occur more frequently when disease prevalence is high.

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Collection and Diagnostic Methods

Specimen: nasopharyngeal swab/aspirate, nasal swab/aspirate/wash, throat swab, bronchoalveolar lavage, sputum.

  • Acceptable specimens vary amongst diagnostic tests

  • Specimens from adults should be collected at the start of symptoms and usually no more than 4 or 5 days later. Very young children can shed influenza virus for more than 5 days.

  • Place specimen in viral transport medium.

  • Transport specimen on wet ice.

  • Specimens can be stored at 2-8º C and tested within 48 hours.

  • Specimens can be frozen at -80º for prolonged periods of time. Avoid multiple freeze-thaws since this results in a decrease in viral titer.

Table 1. Diagnostic Methods for Influenza* (Open Table in a new window)

Method

Influenza Types Identified

Test Time

CLIA Waived?

Viral culture (conventional)

A and B

3-7 days

No

Rapid culture (shell vial)

A and B

1-3 days

No

Immunofluorescence

A and B

2-3 hours

No

* Identification of influenza A subtypes is possible, although not routinely practiced, with these diagnostic methods.

Table 2. Rapid Antigen Tests for Influenza* (Open Table in a new window)

Product (Company)

Influenza Types Identified

Test Time (min)

CLIA Waived?

3M Rapid Detection

Flu A & B Test

(Biomedical Corporation)

A and B

15

No

Alere Influenza A & B

(Alere)

A and B

15

Yes

BD Veritor System for Rapid Detection of Flu A +B

(Becton Dickinson)

A and B

10

Yes

Binax NOW

Influenza A & B

(Alere)

A and B

15

Yes

BioSign

Flu A + B

(Princeton BioMedtech)

A and B

15

No

Directigen EZ

Flu A + B

(Becton Dickinson)

A and B

15

No

OraSure QuickFlu Rapid A & B Test

(Orasure)

A and B

10

No

OSOM

Influenza A & B

(Sekisui)

A and B

10

No

QuickVue

Influenza Test

(Quidel)

A or B

10

Yes

QuickVue

Influenza A + B

(Quidel)

A and B

10

Yes

SAS FluAlert A & B

(SA Scientific)

A and B

15

No

SAS FluAlert A

(SA Scientific)

A

15

Yes

SAS FluAlert B

(SA Scientific)

B

15

Yes

Sofia Influenza A+B

(Quidel)

A and B

15

Yes

TRU FLU

(Meridian Bioscience)

A and B

15

Yes

XPECT Flu A & B

(Remel /Thermofisher)

A and B

15

No

* List may not include all test kits approved by the US Food and Drug Administration (FDA). Subtypes of influenza A are not identified.

 

Table 3. FDA Approved Molecular Tests for Influenza* (Open Table in a new window)

Product

(Company)

Influenza Types Identified

Influenza A Subtypes Identified

Test Time

(h)

CDC Human Influenza Virus Panel

(CDC)

A and B

2009 H1N1

H1

H3

H5

4

eSensor

Respiratory Viral Panel

(GenMark Diagnostics)

 

A and B

2009 H1N1

H1

H3

6

FilmArray

Respiratory Panel

(Biofire)

A and B

2009 H1N1

H1

H3

1

Ibis PLEX-ID Flu

(Ibis/Abbott)

A and B

2009 H1N1

H1

H3

8

IQuum Liat Influenza A/B Assay

(IQuum)

A and B

None

0.5

Prodesse

PROFLU +

(Hologic)

A and B

None

4

Prodesse

ProFAST +

(Hologic)

A

2009 H1N1

H1

H3

3

Quidel Molecular Influenza A +B Assay

(Quidel)

A and B

None

4

Qiagen Artus Influenza A/B Rotor-gene RT-PCR kit

(Qiagen)

A and B

None

4

Simplexa

Influenza Test A/B & RSV

(Focus Diagnostics)

A and B

None

4

Simplexa

Influenza Test A/B & RSV Direct

(Focus Diagnostics)

A and B

None

2

Simplexa

Influenza 2009 H1N1

(Focus Diagnostics)

A

2009 H1N1

4

U.S. ArmyJBAIDS Influenza A/H5

(Biofire)

A

H5N1 (Asian Lineage)

4

U.S. ArmyJBAIDS Influenza A & B

(Biofire)

A and B

None

4

U.S. ArmyJBAIDS Influenza A

(Biofire)

A

2009 H1N1

H1

H3

4

Verigene

Respiratory Virus Nucleic Acid Test

(Nanosphere)

A and B

None

3.5

Verigene

Respiratory Acid Nucleic Acid Test RV+

(Nanosphere)

A and B

2009 H1N1

H1

H3

3.5

Xpert Flu Assay

(Cepheid)

A and B

2009 H1N1

1

xTAG Respiratory Viral Panel

(Luminex)

A and B

H1

H3

8

xTag Respiratory Virus Panel-FAST

(Luminex)

A and B

H1

H3

H5 (RUO)

6

* List may not include all test kits approved by the FDA.

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Background

Description

In recent years, companies have introduced a number of rapid antigen assays, immunofluorescent reagents, rapid viral culture methods, and molecular tests for influenza virus. Some of the molecular methods can rapidly determine influenza A subtypes, which can be useful in determining the potential for resistance to some of the antiviral agents used in therapy. [1]

Indications/Applications

Diagnostic tests for influenza are useful in establishing a diagnosis and in the management of patients who have signs and symptoms compatible with influenza. They are also used to determine whether outbreaks of respiratory disease are due to influenza.

The susceptibility of influenza virus types and subtypes varies by antiviral (Table 4). Some of the molecular tests can rapidly provide the influenza type and subtype data.

Table 4. Susceptibility Profile of Influenza Types and Subtypes to Antiviral Agents* [2] (Open Table in a new window)

 

Amatadine

Rimantidine

Oseltamir

Zanamivir

2009 H1N1

resistant

resistant

sensitiveA

sensitive

H1N1 seasonal flu A

sensitive

sensitive

resistant

sensitive

H3N2 seasonal flu A

resistant

resistant

sensitive

sensitive

Influenza B

resistant

resistant

sensitive

sensitive

* A small number of 2009 H1N1 cases (approximately 2%) with resistance to oseltamir have been detected worldwide and in the United States. [2]

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Considerations

See the list below:

  • Rapid antigen tests, immunofluorescent tests, and virus culture have been reported to often lack in assay sensitivity, specificity, testing time, and ability to subtype for influenza compared to molecular methods. [3]

  • Rapid antigen tests generally have a sensitivity of 50-70% and a specificity of 90-95%. Limited studies have demonstrated very low sensitivity for detection of 2009 H1N1 with some commercial brands. [4, 5, 6, 7, 8, 9]

  • Immunofluorescent tests, with nasopharyngeal specimens, have been reported to have high sensitivity and specificity for identification of influenza A and B. [10]

  • Very early and very late in respiratory season, and when disease prevalence in the community is low, positive diagnostic test results should be confirmed by an alternate method, such as viral culture or a molecular test. [11]

  • Hospitalized patients with a serious respiratory condition should preferably be tested by a molecular method for influenza. [11]

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