The importance of blood volume cultured on detection of bacteraemia

The effect of culturing 2 and 5 ml of blood in 18 ml of supplemented peptone broth I (SPB I) and 45 ml of supplemented broth II (SPB II) respectively, was compared. A total of 204 isolates were recovered from 78 patients. There were 136 isolates recovered from both the 45 and the 18 ml tubes. 20 isolates from the 18 ml tube only and 48 isolates from the 45 ml tube only. Both Gram-negative bacilli and Gram-positive cocci were recovered more frequently from the 45 ml tube than from the 18 ml tube (p less than 0.05). From patients with two or more positive blood cultures the diagnosis of bacteraemia would not have been made in 5 out of 53 patients (9.4%) if only the small culture tube had been used.