A common medical myth is that the yield of BCs is highest when obtained around the time of a fever spike. In 1989, an abstract reported a non-significant trend toward higher frequency of positive BCs in the period immediately before a fever spike¹. In 1994, another study found no significant difference between the yield of simultaneous and serial (separated by a few hrs) BCs², supporting the current practice of collecting ≥2 sets of BCs simultaneously.

In 2008, a multicenter retrospective study found that the likelihood of detecting bacteremia was not significantly enhanced by collecting BCs at the time of fever³.  Instead, obtaining an adequate blood volume (~40 – 60mL for each episode), and collecting ≥2 sets of BCs under strict aseptic technique were emphasized⁴. BCs should be obtained prior to antibiotic administration.

So in our patient, BCs should be obtained if sepsis is suspected, irrespective of fever.

References

1. Thomson RB, et al. Timing of blood culture collection from febrile patients. Abstr. C-227. 89th Annual Meeting American Society of  Microbiology, Washington, DC, 1989. 
2. Li J, et al.  Effects of volume and periodicity on blood cultures. J Clin Microbiol. 1994; 32:2829-2831. 
3. Riedel S, et al. Timing of specimen collection for blood cultures from febrile patients with bacteremia. J Clin Microbiol. 2008;46:1381-1385.
4. Clinical and Laboratory Standards Institute (CLSI). Principles and Procedures for Blood Cultures: Approved Guideline. 2007. CLSI document M47-A. Clinical and Laboratory Standards Institute, Wayne, PA

Contributed by Henrietta Afari, MD, Mass General Hospital, Boston, MA