Investigations
1st investigations to order
no initial test
Test
Usually no tests are needed.
Result
clinical diagnosis
Investigations to consider
FBC
Test
WBC count may be raised with lymphocytosis in viral infections.
An FBC is not routinely indicated.
Result
increased WBC count, lymphocytosis
throat swab
Test
Only justified if McIsaac score of 2 to 3 or more is present.
Result
positive for Streptococcus
sputum culture
Test
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
heterophile antibody test
Test
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
C-reactive protein (CRP)
Test
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
chest x-ray
Test
Indicated if signs/symptoms suggestive of lower respiratory tract spread. Not indicated as first-line investigation.
Result
no change with uncomplicated infection
sinus CT scan
Test
Indicated in cases of chronic maxillary or forehead pain and clinical history compatible with sinusitis.
Radiological investigations are not routinely indicated in the common cold.
Result
air fluid level may be present in sinusitis
viral testing
Test
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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