Investigations

Your Organisational Guidance

ebpracticenet urges you to prioritise the following organisational guidance:

Prévention de l’InfluenzaPublished by: Groupe de travail Développement de recommandations de première ligneLast published: 2018Preventie van influenzaPublished by: Werkgroep Ontwikkeling Richtlijnen Eerste Lijn (Worel)Last published: 2018

1st investigations to order

clinical diagnosis

Test
Result
Test

There are no pathognomonic features of influenza, and further testing is indicated only when the results are likely to affect diagnosis and treatment decisions and to provide community disease surveillance.[82]​​[86]

Result

febrile respiratory illness during a known seasonal influenza outbreak

Investigations to avoid

broad respiratory pathogen panels

Recommendations
Rationale
Recommendations

Do not order broad respiratory pathogen panels, including comprehensive viral panel testing, unless the result will directly influence management decisions or if the patient is hospitalized or considered high risk (e.g., immunocompromised).[91][92]

Rationale

Influenza is a clinical diagnosis and usually does not require confirmatory testing.[82]​ There is a lack of consistent evidence to demonstrate the impact of comprehensive viral panel results on clinical outcomes.[93]

serology

Recommendations
Rationale
Recommendations

Do not use serologic testing to diagnose influenza or to inform clinical decision making.[2][82]

Rationale

Results from a single serum specimen cannot be reliably interpreted, and collection of paired sera 2 to 3 weeks apart is required.[2]

Investigations to consider

molecular assays

Test
Result
Test

Includes rapid molecular assays, reverse-transcription polymerase chain reaction (RT-PCR), and other nucleic acid amplification tests (NAATs).[82]

The Infectious Diseases Society of America recommends using rapid molecular assays for detection of influenza viruses in respiratory specimens of outpatients and RT-PCR or other molecular assays for detection in respiratory specimens of hospitalized patients.[2]

NAATs are the preferred method for detection of influenza virus in clinical samples because of their superior diagnostic sensitivity compared to rapid antigen tests.[90]​

Nasopharyngeal specimens are recommended for a respiratory specimen for viral isolation.[2]

Result

detection of influenza virus; some assays can identify influenza virus types and specific influenza A virus subtypes

antigen detection tests

Test
Result
Test

Includes rapid influenza diagnostic tests and immunofluorescence assays.[82]

Rapid influenza diagnostic tests have high specificity (90% to 99%), but sensitivity is low (50% to 75%).[2][90]​

Result

detection of influenza virus

viral culture

Test
Result
Test

Definitive test for laboratory diagnosis, but takes 3-10 days for results to be reported, so is not often used for initial clinical management. It is used for confirming screening tests and for public health surveillance.

Shell vial (centrifuge-enhanced) culture, if available, may reduce time for results to 1-3 days.[82]​​

Acceptable specimens include throat or nasopharyngeal swab, nasopharyngeal aspirate or wash, and sputum.[90]

Result

detection of seasonal influenza virus or viral antigen

chest x-ray

Test
Result
Test

Should be done if either a primary viral or secondary bacterial pneumonia is suspected.

The radiographic appearances of community-acquired pneumonia include lobar consolidation, interstitial infiltrates, and cavitations.

It is commonly thought that lobar consolidation is suggestive of bacterial pneumonia and interstitial infiltrates are suggestive of pneumonia due to Pneumocystis jirovecii (formerly P carinii) and viruses. However, radiologists cannot reliably differentiate bacterial from nonbacterial pneumonia on the basis of the radiographic appearance alone.[102]

Result

normal in uncomplicated cases; may show infiltrates consistent with pneumonia in complicated cases

Use of this content is subject to our disclaimer