Effects of volume and site of blood draw on blood culture results

Blood culture contamination greatly affects clinical decisions. Hence, it is of interest to assess the influence of factors such as the volume of blood drawn and the site of blood draw on the rates of blood culture contamination. In a retrospective study, blood cultures from infants and children up to 18 years of age who had at least one positive blood culture during the year 2006 were analyzed for their volume of blood drawn, patient's weight, site of blood draw used, and blood culture results. Blood cultures were deemed adequate collections if they contained an appropriate weight-related volume of blood. Moreover, blood culture results were categorized as true pathogens, contaminants, and negative cultures; these were then compared and analyzed with respect to their volume and site of blood draw. A total of 5,023 blood cultures were collected during 2006, of which 843 were analyzed. There were 306 (36%) positive cultures among the 843 cultures analyzed. Of the 306 positive cultures, 98 (32%) were contaminants and 208 (68%) cultures grew significant pathogens. Thirty-five percent of the contaminant cultures had adequate volume compared to 60% in the true bacteremia group (P <0.001). Also, of the 843 cultures, the rates of contamination among the different sites of blood draw were as follows: peripheral venipuncture, 36%; arterial, 10%; and central venous access, 7% (P = 0.155). The rate of contamination was higher with lower blood volumes, and there was no significant difference in the rates of contamination among the different sites of blood draw.