Sufficient Blood Culture Volume

In reading the guideline “Evaluation and Management of Well-Appearing Febrile Infants 8 to 60 Days Old,”1 I hoped the authors would have commented on the importance of technical aspects of blood cultures: both sample volume and ideal minimum sample to broth ratios.

The consideration of the technical aspects of blood cultures is within the scope of the guideline because of the emphasis placed on IMs. The volume of blood required for IMs can exceed that required for more typical laboratory studies (complete blood cell count, etc). In cases in which limited volumes of blood are collected, a common challenge in young infants, any blood sent for IMs might decrease the blood volume included in the blood culture. Data suggest that the concentration of bacteremia is low in infants,2 current practice results in small volumes of blood obtained for culture,3 and rates of pathogen identification are improved with larger amounts of sample obtained.4

The role of IMs in decision-making should be viewed in a historical context. In the article recommending the “step-by-step” approach to management of young infants, 7 of the 61 children (11%) aged 21 to 90 days old with “invasive bacterial infection” were not identified by the step-by-step approach.5 This compares with the 1 of 9 children (11%) aged 0 to 8 weeks old not identified by clinical examination alone in the seminal work by Roberts in 1977.6 I wonder if the subcommittee missed an opportunity to weigh the clinical benefits of decision-making pathways relying on IMs versus the importance of sufficient blood culture volumes. Although portions of a milliliter of blood diverted for IMs or other “routine” laboratory studies may seem trivial, it might be significant when data suggest that <1 mL of blood is frequently submitted for culture.3