Investigations

1st investigations to order

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Result
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Usually no tests are needed.

Result

clinical diagnosis

Investigations to consider

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Result
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WBC count may be elevated with lymphocytosis in viral infections.

A CBC is not routinely indicated.

Result

increased WBC count, lymphocytosis

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Result
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Only justified if McIsaac score of 2 to 3 or more is present.

Result

positive for Streptococcus

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Result
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May be justified in persistent infection with spread to lower respiratory tract.

A sputum culture is not routinely indicated.

Result

positive culture for bacterial pathogen

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Result
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Also known as Monospot test, heterophile agglutination test, or Paul Bunnell test.

Definitive test for infectious mononucleosis.

Heterophile antibodies are present in about 80% to 90% of people with infectious mononucleosis.

Indicated in a patient presenting with extreme tiredness or persisting symptoms.

Result

positive heterophile antibodies

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Result
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CRP is an acute-phase response marker and in the correct clinical context is a surrogate marker of infection.

A CRP is not routinely indicated.

Result

high CRP may indicate more serious infection

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Result
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Indicated if signs/symptoms suggestive of lower respiratory tract spread. Not indicated as first-line investigation.

Result

no change with uncomplicated infection

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Result
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Indicated in cases of chronic maxillary or forehead pain and clinical history compatible with sinusitis.

Radiologic investigations are not routinely indicated in the common cold.

Result

air fluid level may be present in sinusitis

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Result
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Viral testing is sought only as part of research or as a tool for the early diagnosis of influenza during a pandemic.

Rapid viral testing may be useful as confirmation of viral (rather than bacterial) infection, but is not routinely indicated.

Result

confirmed viral infection

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