Central line-associated bloodstream infection — FFICM MCQ

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ModerateSepsisCentral line-associated bloodstream infectionFFICM

A 55-year-old man receiving parenteral nutrition develops fever and rigors during infusion through a tunnelled central line. He is stable but has no respiratory, urinary or abdominal source. The line site is clean. The ICU team wants to confirm whether the line is the source before deciding on removal. What is the most appropriate investigation?

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Correct answer: B — Paired peripheral and catheter blood cultures

The correct answer is B, paired peripheral and catheter blood cultures. In a stable patient on parenteral nutrition with fever and rigors, an intact, clean line site, and no other identifiable source, catheter-related bloodstream infection (CRBSI) is the leading differential, and UK intestinal failure guidance recommends simultaneous quantitative or qualitative paired blood cultures from a peripheral vein and from the catheter hub, with assessment of differential time to positivity, before deciding on line removal. A culture drawn through the catheter that grows significantly earlier than the paired peripheral sample (typically by more than two hours) is highly specific for CRBSI and allows catheter salvage in many cases rather than automatic removal, which matters greatly for a patient dependent on venous access for nutrition. This paired approach distinguishes true bloodstream infection from simple catheter colonisation or contamination, which a single culture cannot do. Why the other options are wrong: E. Swab the intact catheter insertion site: The exit site is clean with no visible inflammation, so a swab would only reflect skin flora and cannot confirm bloodstream infection or guide the decision on line removal. D. Culture the parenteral nutrition bag: This tests the infusate for extrinsic contamination but does not establish whether the catheter itself is the source of the patient's bacteraemia. C. Request CT chest abdomen pelvis immediately: Imaging is used to exclude other sources of sepsis, but the stem already states there is no respiratory, urinary or abdominal source, so this does not address the specific question of confirming line-related infection. A. Send a single blood culture from the line: A single line culture cannot differentiate colonisation from true CRBSI and provides no comparative timing data, risking unnecessary catheter removal or missed diagnosis. Key point: Paired peripheral and catheter blood cultures with differential time to positivity are the standard method to confirm CRBSI while preserving venous access when the line can be safely salvaged.

Reference: BAPEN, British Intestinal Failure Alliance (BIFA) Recommendations for Catheter Related Blood Stream Infections (CRBSI) Diagnosis, updated June 2024, https://www.bapen.org.uk/pdfs/bifa/recommendations-for-crbsi-diagnosis-updated-june-24.pdf