Validity of earlier positivity of central venous blood cultures in comparison with peripheral blood cultures for diagnosing catheter-related bacteremia in cancer patients.

We carried out a prospective study in two French Comprehensive Cancer Centers (95 and 184 beds, respectively) to assess the validity of a test based on the earlier positivity of central venous blood cultures in comparison with peripheral blood cultures for predicting catheter-related bacteremia. The differences between the times to positivity for the 21 patients with clinical catheter-related bacteremia and the differences between the times to positivity for the nine patients with bacteremia due to another source were compared by the median test. The difference between the median values was significant (P = 0.0003). A receiver operating characteristic curve was constructed to determine the optimum threshold of the test, which appeared to be at the cutoff point of >/=+3 h, with 100% specificity and 81% sensitivity. The positive and negative predictive values obtained with this cutoff point confirmed the efficacy of the test for predicting the presence or absence of catheter-related bacteremia in cancer patients. The cutoff point was then used to post-classify the 68 episodes of bacteremia from an unknown source. The characteristics and clinical course of both the positive and negative post-classified episodes did not show that the test was clearly useful for a large number of clinical presentations. We therefore suggest restricting it to febrile neutropenic cancer patients for whom clinical signs of infection are slight or absent and when the test is positive.