What is the role of lab testing in the diagnosis of Legionnaires disease?

Updated: Aug 24, 2018
  • Author: Burke A Cunha, MD; Chief Editor: Michael Stuart Bronze, MD  more...
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Answer

While pneumonias caused by numerous pathogens share similar laboratory findings, hyponatremia (sodium < 130 mEq/L) secondary to the syndrome of inappropriate antidiuretic hormone (SIADH) is more common in Legionnaires disease (LD) than in pneumonias secondary to other pathogens; however, this is not specific for LD.

Other nonspecific laboratory findings in LD include the following:

  • Early/mildly elevated liver enzymes

  • Highly elevated erythrocyte sedimentation rate (ESR) (>90 mm/h)

  • Highly elevated ferritin levels (>2 times normal)

  • Increased C-reactive protein (CRP) levels (>30 mg/L)

  • Hypophosphatemia (specific to LD excluding other causes of hypophosphatemia) [10]

  • Microscopic hematuria


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