Effect of blood dilution on recovery of organisms from clinical blood cultures in medium containing sodium polyanethol sulfonate

Publisher Website
Google Scholar
Abstract
The standard laboratory protocol that requires blood specimens be diluted with .gtoreq. 10 volumes of media was evaluated. Blood was collected from hospitalized patients, and 1 ml was inoculated into each of 3 vials containing 2.3, 7.3 and 24 ml of BACTEC 6B aerobic medium, resulting in dilutions of 1:4, 1:10 and 1:30, respectively. The 3 test vials were treated identically, and the study was carried out at 4 hospitals. Of the 2550 sets of vials inoculated, 174 were positive with clinically significant isolates from 105 patients. There was no difference in the number of positive cultures recovered by 24 h (67%) or 48 h (90%) from any dilution. These percentages agreed with other reports from BACTEC users. The number of positive vials (139, 144, 147, respectively) at each dilution was not significantly different, indicating that all 3 dilutions showed equal recovery of pathogenic microorganisms. Despite this overall equality, 2 patients, 1 on antibiotic therapy, had correlated cultures which failed to grow at the 1:4 dilution. A 1:4 dilution of blood cannot be recommended unequivocably despite the higher overall recovery rate of positive cultures.