Comparison of recovery of organisms from blood cultures diluted 10% (volume/volume) and 20% (volume/volume)

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Abstract
Blood cultures that were diluted 1:5 (20%, vol/vol) and 1:10 (10%, vol/vol) and contained specimens from patients with suspected septicemia were compared. Streptococcus pneumoniae was recovered significantly more frequently from blood cultures diluted 20%; gram-negative bacilli, group D streptococci, Staphylococcus aureus and Candida spp. were recovered significantly sooner and more frequently from blood cultures diluted 10%. Statistically significant differences in isolation rates represented only a small number of patients for whom the positive cultures affected therapy. As long as at least 2 separate sets of blood cultures are obtained per septic episode from each patient, a 1:5-1:10 blood/vented (aerobic) medium ratio apparently provides acceptable results. Blood cultures diluted 10% seemingly provided greater and faster yields than those provided by blood cultures diluted 20%.