[Usefulness of blood cultures from central venous catheters in the diagnosis of infection of the catheter tip].

Central venous blood cultures, obtained through catheters have been used for diagnosis of tip infections. We prospectively studied in a consecutive way two blood culture techniques. In a group of 23 cases, the first 5 ml of catheter solution was discarded, and in the second group of 41 cases the first 10 ml of catheter solution and blood were used. Colony counts for true positive samples were 100 cfu/ml (median value) with a 95% confidence interval = 5-1000 cfu/ml. Test validation showed for all cases, first and second groups respectively: sensitivity 60%, 50% and 62.5%; specificity 91.1%, 100% and 94.7%; positive predictive values 94.1%, 100% and 93.8%; negative predictive values 73.3%, 85% and 64%. This study had a limited utility in the diagnosis of central venous catheter tip infections. Our results show that the most sensitive technique is culture of initial samples obtained through the venous access, and that a cut-off lower than those used in previous studies should be used.