Impact of monitoring blood volume in the BD BACTEC™ FX blood culture system: virtual volume versus actual volume

• Virtual volumes monitored by BD Epicenter and actual volumes are correlated well.
• Blood culture volumes are unacceptably low.
• The positivity is increased 1.2-fold with a 1-mL increase in actual volume.
• The times to positivity of aerobic and anaerobic bottles show strong correlation.
• Blood culture positivity is affected more by clinical condition than blood volume.

The BACTEC™ FX (BD, USA) has been recently upgraded to measure virtual blood volume (VV) in batches of 25 PLUS Aerobic/F bottles. VVs were compared with manually measured actual volumes (AVs). The mean AV was larger in anaerobic bottles: 2.6 ± 1.9 mL in 2995 Aerobic/F bottles and 3.3 ± 1.8 mL in 3053 Lytic/10 Anaerobic/F bottles (P < 0.001). The VV of Aerobic/F bottles was 2.4 ± 1.4 mL, and there was a significant correlation between the VVs and AVs of each department (P < 0.001). The potential positivity in aerobic bottles increased 1.2-fold with a 1-mL increase in the AV (P < 0.001). AV and VV were consistently less than adequate. Although the proportional effect of volume on positivity can be proven only with the AV, VVs are a reliable substitute for AVs to monitor the overall blood volumes and provide feedback to the individual departments or locations.