We prospectively examined 298 sets (298 aerobic, 299 anaerobic, and 73 resin cultures) of blood cultures from 161 critically ill newborns. The attending physicians were unaware of the study. The mean blood volume per patient (aerobic and anaerobic) was 1.05 (range, 0.11 to 3.04) ml. The mean blood volume per aerobic bottle was 0.53 (range, 0.01 to 1.90) ml. Among aerobic samples 2.7% were less than or equal to 0.1 ml, 16% were less than or equal to 0.3 ml, 33% were less than or equal to 0.4 ml, and 55% were less than or equal to 0.5 ml. For anaerobic cultures the mean blood volume was 0.52 (range, 0.01 to 1.79) ml. Among anaerobic samples 2.7% were less than or equal to 0.1 ml, 15% were less than or equal to 0.3 ml, 35% were less than or equal to 0.4 ml, and 58% were less than or equal to 0.5 ml. Blood volume did not correlate with gestational age, chronologic age, or weight. The mean volume of blood submitted in positive cultures was not significantly greater than that in negative cultures. The blood volume used for culture from ill newborns may be inadequate for detecting sepsis, and the adequacy of currently available culture methods needs to be assessed for the small samples submitted from critically ill newborns.
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