ObjectiveTo determine the relative rates of microbial colonization of individual lumens in triple-lumen central venous catheters (CVCs) and calculate the chance of detecting catheter-related blood stream infection (CRBSI) if only one lumen is sampled.DesignProspective evaluation of CVCs from suspected and nonsuspected CRBSI cases.SettingUniversity teaching hospital.PatientsTriple-lumen CVCs from 50 cases of suspected CRBSI (a raised peripheral white blood cell count, temperature >37°C, and/or local signs of infection at the catheter skin entry site) were evaluated. For comparison, 50 triple-lumen CVCs routinely removed at the end of use were evaluated.MeasurementsIn both groups, peripheral blood cultures were taken before CVC removal. After CVC removal, each lumen was sampledin vitrousing the endoluminal brush, and the tip was then cultured using the Maki roll technique.Main ResultsCVCs causing CRBSI had significant microbial colonization in one, two, or three lumens in ten (40%), ten (40%), or five (20%) cases, respectively. Overall, random sampling of only one lumen in CVCs causing CRBSI had a 60% chance of detecting significant colonization.ConclusionsIf only one CVC lumen is sampled, a negative result does not reliably rule out infection. Each lumen of multiple-lumen CVCs should be considered as a potential source of CRBSI.