Effect of Blood Volume in Standard Anaerobic Blood Culture Bottles of the BacT/ALERT 3D System Used for the Detection of Pathogens and Time to Detection

BACKGROUND Blood volume may profoundly affect the isolation of microorganisms in blood cultures. The effect of blood volume in standard anaerobic bottles of the BacT/ALERT 3D system was investigated. METHODS Adult patients who visited the emergency department and referred for blood culture (n = 824) were enrolled from June to September 2013. Two sets of blood cultures were obtained from each patient. One set consisted of 5 mL that was collected in a standard aerobic bottle (SA5), 5 mL that was collected in a standard anaerobic bottle (SN5), and 10 mL that was collected in a standard anaerobic bottle (SN10). The growth of clinically significant pathogens and the time to detection (TTD) were compared between the SN5 and SN10 samples. RESULTS Increasing the volume of blood collected from 5 to 10 mL yielded a 14.7% improvement in the isolation of microorganisms. There was a statistically significant difference in the isolation of pathogens (14 vs. 30, P = 0.023) between the SN5 and SN10 samples. Gram-positive microorganisms were detected earlier in the SN10 samples than the SN5 samples (P = 0.052). The mean TTD of all pathogens was 13.5 h for the SN5 samples and 12.9 h for the SN10 samples (P = 0.099). CONCLUSION Increased blood volume in the SN bottle yielded a significantly higher pathogen detection rate. However, there was no difference in the frequency of earlier detection or TTD between the SN5 and SN10 samples.