Effect of number of blood cultures and volume of blood on detection of bacteremia in children.

Objective: To determine whether bacteremia can be detected more rapidly and completely by (1) obtaining two blood cultures instead of one and/or (2) collecting a larger volume of blood.

Study Design: Prospective comparison of different strategies in 300 patients undergoing blood culture for suspected bacteremia. Each patient had two samples of blood, A (2 ml) and B (9.5 ml), obtained sequentially from separate sites. The B sample was divided into three aliquots: B1 (2 ml), B2 (6 ml), and ISO (1.5 ml, quantitative culture).

Results: A pathogen was isolated from one or more blood cultures in 30 patients (10% of cases). When measured at 24 hours, the pathogen recovery rate for the B2 sample (72%) was higher than that for the individual small-volume samples (A = 37%, B1 = 33%; p < 0.01 for each comparison) and for the combination of the two small-volume samples (A + B1 = 47%; p = 0.04). At final (7-day) reading the pathogen recovery rate for the B2 sample (83%) was higher than that for B1 (60%; p = 0.02) and similar to the recovery rate observed with the combination of the two small-volume cultures (A + B1 = 73%; p = 0.55).

Conclusions: Increasing the volume of blood inoculated into blood culture bottles improves the timely detection of bacteremia in pediatric patients and spares the patients the cost and pain of an additional venipuncture.