What is the additional diagnostic yield of multiple blood cultures in evaluating patients with suspected bloodstream infections?

Lee A, et. al.  Detection of bloodstream infections in adults: how many blood cultures are needed?  J Clin Microbiol. 2007 Nov;45(11):3546-8.

Objective: To assess the effect of using three or more blood cultures in diagnosing bacteremia.

Conclusion: Some additional benefit of the 3rd blood culture; marginal additional benenefit of the 4th blood culture, but maybe for some patients.

Methods:  Retrospective study of all blood cultures from consecutive adult patients admitted to two teaching hospitals from 2004 through 2005.  Included patients with 3 or more cultures taken during 24 hour period and whose records indicated true infection rather than specimen contamination.  A possible limitation of the method is that if 2 cultures taken at the same time from two sites were negative and then a third culture was taken later and was positive, the authors counted that as first positive on the third culture even though the positive culture was actually the second time a culture was taken.

Data: Table 2 (p. 3547) summarizes the number of cultures needed to detect common pathogens in unimicrobial infections.  Overall, of the 629 unimicrobial episodes, the percentage of cultures that identified pathogens were:

1 culture 73%
2 cultures: 90%
3 cultures: 98%
4 Cultures:  99.7%

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About Amy

Clinical Informationist at EUH Branch Library
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