What is the role of blood cultures in bacterial pneumonia?

Updated: Sep 30, 2020
  • Author: Justina Gamache, MD; Chief Editor: Guy W Soo Hoo, MD, MPH  more...
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Blood cultures should be obtained before the administration of antibiotics. These cultures require 24 hours (minimum) to incubate. When blood cultures are positive, they correlate well with the microbiologic agent causing the pneumonia.

Unfortunately, blood cultures show poor sensitivity in pneumonia; findings are positive in approximately 40% of cases. Even in pneumococcal pneumonia, the results are often negative. Their yield may be higher in patients with more severe pneumonia/infection.

The findings probably have minimal clinical effect in treating bacterial pneumonia. Indeed, the use of blood cultures only rarely dictates a change in empiric antibiotics.

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