What is the role of lab tests in the workup of pneumonia in immunocompromised patients?

Updated: Jan 07, 2019
  • Author: Julie B Zhao, MD; Chief Editor: Barry E Brenner, MD, PhD, FACEP  more...
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Laboratory studies that should be obtained include a complete blood count (CBC) with differential, basic metabolic panel, arterial blood gas (ABG), lactate dehydrogenase (LDH) level, erythrocyte sedimentation rate (ESR), and C reactive protein (CRP).

If tuberculosis is suspected, sputum culture, sputum Gram stain, acid-fast bacillus (AFB) smear, and AFB culture should be collected while patients are in isolation. 

Two sets of blood cultures, despite their low yield and infrequent impact on care, are considered standard of care. [47, 48]  They are especially important in immunosuppressed individuals as they may at times be the only objective finding of infection.

Recently, procalcitonin (PCT) level has been shown to be a reliable biomarker with good sensitivity and specificity for bacterial causes of pneumonia or other infection. As it is triggered by bacterial endotoxin, procalcitonin levels can be a useful adjuvant to distinguish bacterial etiologies of infection from viral, fungal, or autoimmune causes. Trending of PCT level is also established to be useful for initiating and guiding antibiotic therapy. [49, 50, 51]

Other routine laboratory studies may be clinically indicated, such as viral nasal swabs, urine antigen testing (Legionella pneumophila, Histoplasma capsulatum, Streptococcus pneumoniae), PCR studies (CMV, HHV6), serum antigen testing (cryptococcus, galactomannan), and other assays such as serum 1,3 beta-D-Glucan. [52]

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