In a prospective, randomized clinical trial, the use of lithium-heparin tubes for diversion of blood prior to aspiration of culture led to a 60% decrease in blood culture contamination compared with aspiration after obtaining culture. These study results were published in Clinical Infectious Diseases.
The study randomized orders of blood draws to biochemistry or culture. Blood was either aspirated into a sterile lithium-heparin tube before blood culture bottles (diversion group) or blood cultures first and then lithium-heparin tube (control group). Standard disinfection and venipuncture procedures were used and all personnel except the phlebotomist were blinded.
A total of 970 culture/biochemistry sets were included and analyzed: 480 samples in the control group and 490 in the diversion group. Contamination occurred in 5.0% of samples from the control group vs 2.0% in the diversion group cultures (P =.01). Similarly, in comparing the control vs diversion cultures, true pathogens were identified in 5.4% and 3.7% of samples, respectively (P =.22).
Investigators also found that despite randomization, demographic differences were apparent between groups. A post-hoc analysis of 637 cultures from 610 patients admitted from home neutralized these differences but culture contamination remained more frequent in the control group, 5% vs 2% (P =.03). Further, fewer members of the diversion group were admitted to hospital, 58.5% compared with 66.9% of control participants. Length of stay was also shorter for the diversion group compared with control participants, 22 hours (interquartile range 5-97) vs 30 hours (interquartile range 6-122; P =.02).
According to investigators, after in-depth investigation into study performance, no explanation could be found for the differences in patient populations. Another limitation was the inability to blind the phlebotomist to group assignment and that this was a single center study.
The investigators remarked that, “although obtaining blood cultures as the first tests from venipuncture in order to reduce contamination is a widely accepted practice, it is not evidence-based and the current study shows that it may, in fact, be erroneous.” The results here concluded that diverting the initial blood to an alternative test reduces the incidence of contamination. This intervention can also be performed at minimal cost and is easy, effective, and does not waste blood. The study authors believe that the findings from this single center need to be repeated in multicenter studies and then if verified, inform changes to common practice guidelines.
Zimmerman FS, Karameh H, Ben-Chetrit E, Zalut T, Assous M, Levin PD. Modification of blood test draw order to reduce blood culture contamination: a randomized clinical trial [published online October 1, 2019]. Clin Infect Dis. doi:10.1093/cid/ciz971