EFFECTS OF VOLUME AND PERIODICITY ON BLOOD CULTURES

Blood specimens collected for culture by using the high-volume resin-b ased BACTEC system over an 18-month period at the Seattle Veterans Adm inistration Center were examined in this study. Of 7,783 cultures obta ined, 624 were classified as true positives. Patients in this group ha d between 20 and 60 mi of blood drawn per culture and separated into 1 0-ml aliquots for incubation. Analysis of the results stratified by cu ltured volume and time interval between specimen collection accorded y ield advantage to culture volume at the maximal amounts tested. No adv antage was observed with any particular interval of collection. Increa sing cultured volume from 20 to 40 ml increased yield by 19%. Increasi ng cultured volume from 40 to 60 mi increased yield by an additional 1 0%. The same effect was seen whether cultures were drawn simultaneousl y or serially within 24 h. These observations support other reports de monstrating increased yield with increased cultured blood volume. Howe ver, they demonstrate increases in yield at volumes much higher than p reviously considered. In conclusion, this study demonstrates that high -volume blood cultures drawn serially or simultaneously return the bes t yields.