What is the role of lab testing in the evaluation of community-acquired pneumonia (CAP)?

Updated: Oct 31, 2019
  • Author: Stephanie L Baer, MD; Chief Editor: Michael Stuart Bronze, MD  more...
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Several nonspecific laboratory tests are often performed during the workup of community-acquired pneumonia (CAP), particularly if atypical CAP is suspected.

Serum transaminase, serum sodium, serum ferritin, serum phosphorus, and creatine phosphokinase (CPK) levels may provide evidence supporting a particular pathogen, such as Legionella. Lactic acid, white blood cell (WBC) count, blood urea nitrogen, and creatinine may be used in categorizing the severity of illness.

Cold agglutinin titers of 1:32 or greater may support a diagnosis of M pneumoniae, although this test is neither sensitive nor specific and has largely been replaced by newer diagnostic studies, such as respiratory pathogen PCR assay.

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