Investigations
1st investigations to order
oxygen saturation in air
Test
Low saturation indicates a more severe course of disease requiring hospitalisation.
Result
may be low (<90%)
WBC count
Test
Should be done for patients requiring hospitalisation. Relatively minor elevations in WBC counts (usually <13,000 x 10⁹/L [13,000/microlitre]) in patients with pneumonia suggest an atypical pathogen.
Result
may be slightly elevated; may reveal relative lymphocytosis if infection is viral
haemoglobin
Test
May accompany Mycoplasma pneumoniae infections.
Result
may show anaemia
Liver function tests (LFTs)
Test
Ordered for inpatients; elevated liver enzymes (AST/ALT) suggest Mycoplasma pneumoniae or Legionella pneumophila.
Result
elevated
serum urea level
Test
Elevation in urea suggests more severe disease favouring hospitalisation.
Result
70.7 mmol/L (>198 mg/dL)
real-time reverse transcription polymerase chain reaction (RT-PCR) for SARS-CoV-2
Test
Molecular testing is required to confirm the diagnosis. Nucleic acid sequencing may be required to confirm the diagnosis.[38] Priorities for testing depend on local guidelines and available resources.
Result
positive for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) viral RNA
chest x-ray
Test
May show more extensive abnormalities than physical examination would suggest.
Result
infiltrates
Investigations to consider
urinary Legionella antigen
Test
Indicated in cases of severe pneumonia and when L pneumophila infection is suspected.
Result
may be positive with Legionella angtigen
sputum culture
Test
Indicated in cases of severe pneumonia where cultures of blood and sputum may be required, as well as specific sputum assays and cultures and urine antigen tests for Legionella and Streptococcus pneumoniae.[18] Patients with higher acuity pneumonia such as those requiring hospitalisation and/or ICU care should undergo a sputum gram stain and culture, nasopharyngeal PCR testing, blood cultures and be considered for Legionella urinary antigen testing.
Result
may be positive with Legionella or Streptococcus pneumoniae
molecular diagnosis of Mycoplasma pneumoniae or Chlamydophila pneumoniae
Test
Either from sputum or throat swabs.
Result
may be positive with M pneumoniae or C pneumoniae
nasopharyngeal PCR
Test
Patients with higher acuity pneumonia such as those requiring hospitalisation and/or ICU care should undergo a sputum gram stain and culture, nasopharyngeal PCR testing, blood cultures and be considered for Legionella urinary antigen testing.
Result
may be positive with viral pneumonia
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