Diagnosis of Catheter-related Bacteraemia: a Prospective Comparison of the Time to Positivity of Hub-blood Versus Peripheral-blood Cultures

Background: A method of diagnosing catheter-related infection (CRI) without removing the catheter would be useful. An earlier positivity of central compared with peripheral venous-blood cultures may be associated with catheter-related bacteraemia. We evaluated prospectively the differential time to positivity (DTP) of paired blood cultures drawn simultaneously via the catheter hub and from a peripheral venous site.

Methods: Over a 14-month period in an intensive-care unit of a cancer referral centre, simultaneous hub-blood and peripheral-blood cultures (a mean of two per patient) were obtained from patients with a suspected CRI. According to clinical criteria and quantitative culture of the catheter tip, cases were classified as CRI or sepsis of other origin. At least one pair of hub-blood and peripheral-blood cultures was obtained within 48 h before catheter removal, and we recorded the DTP between hub-blood and peripheral-blood cultures with an automatic device for detection of blood culture positivity.

Findings: We analysed 93 catheters removed because of suspicion of CRI. In 28 episodes, the same micro-organisms were found in both hub-blood and peripheral-blood cultures. A diagnosis of definite bacteraemic CRI was made in 16 of the 17 patients in whom a positive hub-blood culture was detected at least 2 hours earlier than peripheral-blood culture. About half (9/17) of these episodes occurred in long-term (>30 days) devices. CRI was excluded in ten of the 11 patients with a DTP lower than 2 h. The DTP of paired blood cultures was significantly greater in patients with CRI than in others (p<10(-4)). A cut-off DTP value of 120 min had 91% specificity and 94% sensitivity for the diagnosis of CRI. Three of 17 episodes with only hub-blood culture positive were associated with CRI.

Interpretation: This prospective study suggests that measurement of the differential time to positivity between hub-blood and peripheral-blood cultures is a simple and reliable tool for in-situ diagnosis of catheter-related sepsis in cancer patients. Further studies are needed to confirm these data for short-term catheters.