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Can Procalcitonin Distinguish Viral vs Bacterial Pneumonia?

August 1, 2019

Written by Thomas Davis

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Procalcitonin is not sufficiently accurate for ruling in or out bacterial pneumonia.

Why does this matter?
In 2017, the US Food and Drug Administration approved procalcitonin for guiding antibiotic therapy in acute respiratory infections. Studies have shown that procalcitonin falls rapidly during recovery from bacterial infections, which may limit exposure to antibiotics. Now, some physicians are using procalcitonin to discontinue antibiotics before they’re even started. There’s no doubt that #procalcitonin is trending among our colleagues when we admit for pneumonia. But how reliable is it at differentiating bacterial from viral pneumonia?

Is #procalcitonin for pneumonia fake news?
This was a meta-analysis of 12 studies that included 2,408 patients diagnosed with community acquired pneumonia. The included studies microbiologically confirmed a specific etiology (i.e. viral vs bacterial). Using a serum procalcitonin cutoff of 0.5 ug/L, the sensitivity of procalcitonin was 0.55 (95% CI = 0.37 – 0.71). The specificity of procalcitonin was 0.76 (95% CI = 0.62 – 0.86). Of course, lowering the procalcitonin cutoff would improve the sensitivity of procalcitonin. This would possibly allow antibiotics to be avoided altogether. Unfortunately, even this strategy may fall short. According to this study that was included in the meta-analysis, a low procalcitonin may help rule out typical bacterial pneumonia. However, it appears that atypical bacterial pathogens produce extremely low procalcitonin levels, which makes it impossible to differentiate them from viruses.

Procalcitonin to distinguish viral from bacterial pneumonia: A systematic review and meta-analysis. Clin Infect Dis. 2019 Jun 25. pii: ciz545. doi: 10.1093/cid/ciz545. [Epub ahead of print]

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Reviewed by Clay Smith

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