Investigations

1st investigations to order

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Result
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May show more extensive abnormalities than physical exam would suggest.

Result

infiltrates

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Result
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Should be done for patients requiring hospitalization. Relatively minor elevations in WBC counts (usually <13,000/microliter) in patients with pneumonia suggest an atypical pathogen.

Result

may be slightly elevated; may reveal relative lymphocytosis if infection is viral

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Result
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May accompany Mycoplasma pneumoniae infections.

Result

may show anemia

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Result
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Ordered for inpatients; elevated LFTs suggest Mycoplasma pneumoniae or Legionella pneumophila.

Result

elevated

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Result
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Low saturation indicates a more severe course of disease requiring hospitalization.

Result

may be low (<90%)

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Result
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Elevation in blood urea nitrogen suggests more severe disease favoring hospitalization.

Result

>198 mg/dL

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Result
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Molecular testing is required to confirm the diagnosis. Nucleic acid sequencing may be required to confirm the diagnosis.[37] Priorities for testing depend on local guidelines and available resources.

During the pandemic, consider all patients with cough and fever or suggestive symptoms to have COVID-19 until proven otherwise. See our topic Coronavirus disease 2019 (COVID-19).

Result

positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral RNA

Investigations to consider

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Result
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Indicated in cases of severe pneumonia and when L pneumophila infection is suspected.

Result

may be positive with Legionella antigen

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Result
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Indicated in cases of severe pneumonia and when L pneumophila infection is suspected.

Result

may be positive with Legionella

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Result
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Either from sputum or throat swabs.

Result

may be positive with M pneumoniae or C pneumoniae

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Result
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Requires blood from early in the course of disease and a second blood specimen at least 10 days later. May be used to confirm diagnosis of many atypical pathogens and some viruses. In most cases, serology will be the main diagnostic test for Coxiella burnetii pneumonia.[36]

Result

rise in titer on convalescent serum

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Result
Test

Viruses can cause atypical pneumonia but may be difficult to culture and results may take days to return.

Result

may be positive with viral pneumonia

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