The accuracy of paired quantitative blood cultures (PQtBCs) collected in pediatric Isolator 1.5-ml tubes compared to central venous catheter (CVC) segment cultures (hub and tip) to diagnose catheter-related bacteremia (CRB) was evaluated in 58 bacteremic adult patients. The second aim of this study was to state precisely whether the tip or the hub (or both) of the infected device was the source of the bacteremia in case of significant results of PQtBC. Fifty-eight bacteremic patients with suspected CRB entered the study. In 52 patients, the diagnosis was obtained before CVC removal by PQtBC and was confirmed by CVC segment cultures: CRB in 30 patients, non-catheter-related bacteremia in 22 patients. Six patients had CRB not found by PQtBC. 1) PQtBC is 83% sensitive, 100% specific (negative predictive values 78%, positive predictive values 100%). 2) Sixteen bacteremic patients had authentic hub-related bacteremia (positive hub culture associated with negative tip cultures). When CRB is suspected in bacteremic patients, a negative tip culture cannot exclude the diagnosis of CRB. In all cases, CVC tip culture must be associated either with PQtBC or with hub cultures.