Optimized pathogen detection with 30- compared to 20-milliliter blood culture draws

Using data from 23,313 patients, we assessed whether two blood culture sets of three bottles per set would detect more pathogens than two sets of two bottles per set and achieve similar sensitivity to collecting three sets of two bottles per set. We also compared the yield of aerobic and anaerobic bottles. Thirty milliliters of blood was distributed to one anaerobic and two aerobic bottles. Among 26,855 collections of ≥60 ml within 30 min, 1,379 (5.1%) were positive for a pathogen not requiring detection in more than one set to be considered a pathogen, with 72 additional distinct pathogens detected using two 30-ml compared to two 20-ml sets of one aerobic and one anaerobic bottle (increased yield, 7.9%; 95% confidence interval [CI], 6.2 to 9.8%). For conditional pathogens requiring detection in at least two positive blood cultures for classification as pathogens (i.e., otherwise classified as contaminants), there were 162 positive detections with two 30-ml sets, of which 16 would not have been detected by two 20-ml sets (increased yield, 11.0% [95% CI, 6.4 to 17.2%]). Among 134 subjects who had three sets of 30 ml each within a 30-min interval, there was complete concordance between 60 ml of blood drawn in the first two sets of 30 ml and three 20-ml sets (P = 1.0). One aerobic bottle plus one anaerobic bottle yielded more pathogens than two aerobic bottles for organisms requiring a single (P < 0.001) and two (P = 0.04) positive sets to be defined as pathogens. In conclusion, we showed that collection of two aerobic and one anaerobic blood culture bottles per set results in improved yield compared to two bottles per set. We also confirmed that an anaerobic bottle should be included in blood culture sets.