Comparison of arterial and venous blood samples for the diagnosis of bacteremia in critically ill patients

: We compared the blood culture results obtained either by venipuncture or through an arterial catheter in 51 critically ill patients with 217 clinically suspected episodes of bacteremia. During each episode, three blood culture samples, two arterial and one venous, were drawn within 1 h. One or more cultures were positive in 42 (19%) of the episodes, but there were great discrepancies between the results obtained by the two methods. In only eight cases did both methods give the same microorganism. In eight other episodes, the two arterial cultures were positive while the venous sample was negative, probably indicating a continuous contamination of the catheter system. Pseudomonas aeruginosa and Staphylococcus epidermidis were the two most common microbes. The frequency of positive arterial catheter blood cultures did not increase with the length of catheter use. We conclude that an arterial catheter is not a reliable sampling site for blood cultures and does not replace the conventional venipuncture method.