Blood cultures (BC) drawn through valved catheter hubs have a 10-20% positivity rate with the majority being false positives. Sherertz R, Karchmer T, Palevacino E, Bischoff W. Wake Forest University School of Medicine, Winston-Salem, NC

Background: In recent years concerns have been raised that valved catheter hubs may increase the risk of bloodstream infection (BSI). Previously when our own BSI rates increased after the introduction of a valved hub, we studied the frequency of internal hub contamination associated with such hubs and found it to be high.

Objective: This study was designed to determine the likelihood that a positive blood culture drawn through a catheter hub is a false positive.

Methods: Over a four year period we evaluated the risk of contamination associated with three different types of valved catheter hubs. The initial blood drawn through a catheter hub prior to the clinical specimen was cultured in a Dupont Isolator BC tube. Results of these BC, designated hub BC, and the clinical BC from the same patients were analyzed further to determine the relationship between hub contamination and true BSI.  

Results: Hub BC drawn through Clearlink© catheter hubs were twice as likely to be positive as hub BC drawn through Clave© or Qsyte© hubs (118/344 - 21.8% vs 58/256 - 10.9% vs 136/437 - 10.5%, respectively; P<0.04). Pathogens were isolated 45% of the time and skin organisms 55% of the time from hub BC. The likelihood of a positive hub BC was increased by a higher number of clinical BC done in a 96 hour window surrounding the hub BC and also by a higher number of clinical BC that were positive for the same organism. Of 112 patients with positive hub BC, 18.8% met CDC criteria identified by clinical BC alone, whereas 50% met CDC criteria if hub BC were also included - a 2.7 fold increase. Considering the subgroup who only grew pathogens in hub BC, 58% of these patients had no clinical BC drawn, the average temperature was lower than for patients growing pathogens in clinical BC (99.4 ± 1.3 versus 100.6 ± 1.9, P=0.01), and 92% of the patients who were discharged (13/14) did not receive an antibiotic that would have treated the pathogen that grew.  Based on these findings it was estimated that greater than 50% of the hub BC that were positive may have been false positives, even if a pathogen was isolated.

Conclusions: Clearlink© catheter hubs appear to carry a higher risk of hub contamination compared to Clave© or Qsyte© hubs, but this conclusion requires further study.   The practice of drawing BC through a catheter hub could have nearly tripled the rate of BSIs meeting CDC criteria.  However, our findings suggested that the majority of these BSIs determined by hub BC could be considered false positives.