Should Blood Cultures Be Drawn Through an Indwelling Catheter?

Abstract There is no practical way to definitively diagnose a catheter-related bloodstream infection in situ if blood cultures are only obtained percutaneously unless there is the rare occurrence of purulent drainage from a central venous catheter insertion site. That is why the Infectious Diseases Society of America guidelines for diagnosis and management of catheter-related bloodstream infections and Infectious Diseases Society of America guidelines for evaluation of fever in critically ill patients both recommend drawing blood cultures from a central venous catheter and percutaneously if the catheter is a suspected source of infection. However, central venous catheter–drawn blood cultures may be more likely to be positive reflecting catheter hub, connector, or intraluminal colonization, and many hospitals in the United States discourage blood culture collection from catheters in an effort to reduce reporting of central-line associated bloodstream infections to the Centers for Disease Control and Prevention. As such, clinical decisions are made regarding catheter removal or other therapeutic interventions based on incomplete and potentially inaccurate data. We urge clinicians to obtain catheter-drawn blood cultures when the catheter may be the source of suspected infection.


MAIN POINT
Blood cultures should be collected from a central venous catheter and percutaneously when the catheter is a possible source of infection.
Clinicians in many US hospitals are discouraged from obtaining blood cultures from indwelling central venous catheters (CVCs; personal communication) to reduce the likelihood of positive blood cultures resulting from catheter colonization, which may lead to reporting a central line-associated bloodstream infection to the NHSN surveillance system.The motivation behind this change in practice reflects the fact that central lineassociated bloodstream infections are associated with potential loss of hospital reimbursement from the Centers for Medicare & Medicaid Services and thirdparty payers, as well as potential damage to institutional reputation.However, this practice is based on older studies [1,2] before the increasing use of port protectors [3,4] and conflicts with Infectious Diseases Society of America guidelines [5,6].Additionally, how can a clinician definitively diagnose a catheter-related bloodstream infection (CRBSI) if only percutaneously drawn cultures are obtained unless the patient has purulent drainage from the insertion site (uncommon in patients with infected CVCs; more common with infected short-term peripheral venous catheters), or the catheter is removed and the tip is cultured revealing the same microbe as in the blood?It is also important to remember that CRBSI reflects a dynamic process.Bacteremia or fungemia emanating from a colonized catheter may be intermittent depending on whether or not fluid has been infusing through a colonized catheter lumen, the type of infusate (eg, an antibiotic infused through the catheter lumen just before blood draw may lead to false-negative blood cultures), characteristics of the colonizing microorganism and density of intraluminal microbial growth [7,8], as well as the immune status of the patient (eg, does the patient have a functional liver and spleen to clear pathogens from the bloodstream) [8].When fluids are flowing through a colonized catheter, patients may develop fever or other signs of systemic infection as microbes are pushed into the bloodstream.During such times, peripheral blood cultures may be positive.A patient's symptoms may resolve when the fluids are no longer being infused through the catheter and percutaneously drawn blood cultures may be negative.This scenario is most evident in patients receiving hemodialysis through a central venous catheter who become unwell during dialysis but whose symptoms improve after completion of dialysis.
A positive catheter-drawn blood culture in the absence of growth from a percutaneously drawn culture may reflect Should Blood Cultures Be Drawn Through an Indwelling Catheter?• OFID • 1 Open Forum Infectious Diseases P E R S P E C T I V E S contamination, especially with growth of common skin commensals, or a greater volume of blood drawn from catheters for culture compared with blood cultures drawn from peripheral veins [9].This finding should not be disregarded as contamination in all cases, particularly with growth of microbes commonly causing serious bloodstream infections (eg, Staphylococcus aureus), or hemodynamically unstable patients without an alternative explanation for their symptomatology.Repeat blood cultures may be indicated with continued symptoms without a clear source.Additionally, in patients with longterm catheters, this finding may be a signal that the catheter is colonized and clinicians may consider catheter lock therapy in an effort to eradicate colonization of the catheter because studies have demonstrated that without intervention, such patients may go on to have microbial growth from percutaneously drawn cultures over the ensuing weeks [10].When there is growth from both catheter-drawn and percutaneously drawn blood cultures, a differential time to blood culture positivity may assist in identifying the catheter as the source of the bloodstream infection [11].On the other hand, the negative consequences of blood culture contamination should not be dismissed as blood culture contamination is clearly associated with extended length of hospital stay, inappropriate antibiotic use, and diagnostic confusion [12].
When encountering a patient with possible CRBSI, a pertinent question is how many lumens should be sampled if the CVC is thought to be a likely source of infection.This is important because many critically ill patients with fever or sepsis have multiple intravascular catheters, often with multiple lumens.Sampling each lumen could result in many blood cultures leading to increased cost, iatrogenic anemia, and additional opportunities for contamination.However, approximately one-third of CRBSIs will be missed if 1 lumen of a multilumen catheter is sampled [13].Despite controversy regarding which lumen and how many lumens should be sampled for blood culture collection, the lumen used for administration of total parenteral nutrition and/ or blood products may have the highest yield [14].Initially performing only peripheral blood cultures in patients with suspected sepsis and then going back to obtain catheter-drawn cultures to establish the catheter as the source has substantial downsides.First, after obtaining initial blood cultures, in many instances, empiric antimicrobial therapy will be initiated, making subsequent cultures from the catheter less reliable.Second, delay in diagnosis of CRBSI could result in a delay in removal of an infected catheter with poor source control and greater chance for metastatic spread and poor outcome.Accurate assessment of which lumen(s) are involved is particularly important if an attempt at catheter salvage with catheter lock therapy is contemplated.

RECOMMENDATIONS
• Percutaneously drawn blood cultures should be obtained when blood cultures are indicated.
Dr. Mermel is on the Scientific Advisory Board of Citius Pharma and serves as a consultant for CorMedix.Dr. Rupp has received research funding from Magnolia Medical Technologies, Contrafect, and NIH/ Duke Clinical Research Institute and has served as a consultant or on an advisory board for Citius Pharmaceuticals, 3M, and Teleflex.
NotesAcknowledgments. There was no funding for this work.Potential conflicts of interest.