Teachable Moment 

Less Is More

October 21, 2024

The Harm of Inappropriate Central Line Blood Cultures in Clinical Practice

Alexandra N. Fuher, Heather Young, Mark E. Mikkelsen

JAMA Intern Med. Published online October 21, 2024. doi:10.1001/jamainternmed.2024.5344

A57-year-old man with end-stage kidney disease who was receiving hemodialysis through a tunneled central venous catheter presented to the emergency department with severe hyperkalemia that prompted admission for emergent hemodialysis. He was also found to have community-acquired pneumonia, as diagnosed by a left upper lobar alveolar infiltrate and acute hypoxemic respiratory failure. An initial infectious workup included 2 peripheral blood cultures, and treatment with ceftriaxone and azithromycin was initiated. He then became febrile (temperature, 38.1 °C), and blood culture specimens were collected from the central venous catheter and a peripheral source. After 1 day, the blood culture specimen from his central line grew coagulase-negative Staphylococcus via blood culture multiplex polymerase chain reaction, and vancomycin was added. The next day, 2 additional peripheral blood culture specimens were collected. The infectious diseases service was consulted for possible catheter related bloodstream infection (CRBSI). The consultant determined that the risk of CRBSI was low because the tunneled line was nontender without surrounding erythema or drainage, and the patient had a known alternative source of infection. They recommended discontinuation of vancomycin and completion of the 5-day course of antibiotic therapy for pneumonia. Initial and repeated peripheral culture results remained negative, his fever and hypoxia resolved, and the patient was successfully discharged.

Collection of blood cultures from central line catheters, in the absence of any concern for a CRBSI, has been shown to lack benefit and be associated with potential harms.¹ In this case, blood culture specimens taken from the central line was followed by a false-positive blood culture result (eg, absence of true bacteremia) and contributed to additional laboratory testing, specialty consultation, unnecessary antibiotics, and an extended duration of hospitalization. Blood cultures from central lines are not the optimal test for bacteremia. In a systematic review, catheter blood draws, compared with venipuncture, were associated with increased odds of false-positive blood culture results, with a mean odds ratio of 2.69 (95% CI, 2.03-3.57).² Furthermore, a retrospective observational study comparing paired catheter-drawn and peripheral blood cultures found that in only 2 cases (0.2%) was the diagnosis of bacteremia made on catheter culture results alone.³ False-positive blood culture results are often due to skin contaminants, such as coagulase-negative staphylococci.¹ Reducing false-positive blood culture results is important given the numerous potential downstream adverse effects. Patients with false-positive culture results often receive unnecessary antibiotics, which is associated with an increased risk of potential harms, including development of antimicrobial-resistant organisms, secondary infections (eg, Clostridium difficile), and adverse drug reactions, such as acute kidney injury and severe cutaneous reactions (eg, Stevens-Johnson syndrome).¹ Although not experienced in the case previously described, patients with false-positive blood culture results are more likely to experience unnecessary line removal, unnecessary testing (such as repeated blood cultures or echocardiogram), and delayed diagnosis. Furthermore, the economic consequences of false-positive blood culture results include increased length of stay, averaging 1 to 5.4 additional days, and increased total cost of hospitalization, averaging an additional $4500 to $10 078.¹ The most recent Society of Critical Care Medicine and Infectious Diseases Society of America guidelines⁴ affirm the 2009 guidelines⁵ that recommended only obtaining blood culture specimens from a central line when there is concern for a CRBSI. CRBSI should be suspected clinically in patients with an indwelling central catheter and signs or symptoms of systemic infection, including fever, chills, or hypotension, with no other evidence of an alternative source or neutropenic fever. This patient had no signs of CRBSI, and pneumonia was identified as a source of fever; central line sampling was unnecessary in his case. When CRBSI is suspected, guidelines recommend obtaining paired blood culture specimens from the central catheter and peripheral vein before initiating antibiotics, using careful skin and catheter disinfection, and considering time to positivity if both cultures yield positive results.⁴ Differential time to positivity can be used to define CRBSI. If central and peripheral cultures are positive for the same organism, with the former being positive 2 or more hours earlier than the peripheral specimen, a diagnosis of CRBSI is supported. There are challenges using and interpreting differential time to positivity (eg, whether and/or when to discontinue antibiotics if the central culture yields a positive result but the peripheral culture is no growth to date), as discussed in the 2023 guidelines.⁴

Blood cultures from central lines are not associated with a significantly increased likelihood of diagnosing true bacteremia, are associated with higher false-positive rates,⁴ may result in unnecessary medical care, and contribute to increased health care expenses.¹ Understanding the indications for obtaining central line blood culture specimens in clinical practice is important (eg, being unable to obtain peripheral blood draw, suspected CRBSI, or neutropenic fever). Initiatives to improve adherence to evidence-based practices for blood culture collection (eg, modification of the electronic health record to default to peripheral blood cultures and limit central cultures to the aforementioned examples) may improve resource utilization and patient outcomes.¹ This case highlights patient and systemic harms associated with the unnecessary collection of central line blood culture specimens.