Reliability of differential time to positivity technique for diagnosing catheter-related bloodstream infections: a retrospective analysis

The differential time to positivity (DTTP) technique is the recommended conservative procedure to diagnose catheter-related bloodstream infection (C-RBSI). However, its reliability and accuracy remain under debate. Therefore, we aimed to compare the DTTP technique feasibility to detect C-RBSI compared to the catheter culture (CC) method. We conducted a 9-month retrospective study including bacteremic episodes in which both DTTP blood cultures (BC) and CC were obtained. We analyzed the diagnostic validity of the DTTP technique for detecting C-RBSI compared to the gold standard (C-RBSI with CC), along with patient clinical data. We included 37 episodes of C-RBSI where both DTTP BC and CC were obtained. C-RBSI was confirmed by both techniques in only 13 episodes (35.1%), whereas in 11 (29.7%) and 13 (35.1%), only DTTP BC or DTTP BC with CC (with a difference between catheter lumen and peripheral BC growth of <2 hours) was positive, respectively. Therefore, the validity values of the DTTP technique for predicting C-RBSI were as follows: sensitivity, 50.0%; specificity, 71.8%; positive predictive value, 54.2%; and negative predictive value, 68.3%. The distribution of microorganisms was similar among the three groups. All patients in whom colonization was not demonstrated by CC (<i>n</i> = 11) had been receiving antibiotics before catheter withdrawal. DTTP is a conservative technique that might help to diagnose C-RBSI mostly in situations where catheter removal cannot be achieved. However, it should be interpreted with caution and never be used to rule out C-RBSI. CC before starting antimicrobial therapy remains the most reliable method to diagnose and confirm an episode of C-RBSI.IMPORTANCEWe try to clarify the reliability of the differential time to positivity technique to predict C-RBSI. It may be interpreted with caution and considering clinical signs, as some C-RBSI can be misdiagnosed.