Blood cultures
⚠️ Strict asepsis is essential: a skin contaminant (e.g. coagulase-negative staphylococci) can result in unnecessary prolonged antibiotics for a “false” bacteraemia.
👉 Think “contamination = complication.”
🧾 Introduction
- Blood cultures are a key part of the sepsis screen alongside urine culture, CXR, sputum culture and serology.
- Indications: fever, rigors, sweats, delirium, or other signs of sepsis. ⚠️ Some bacteraemic patients may be afebrile.
- Always send two bottles – one aerobic, one anaerobic. If volume limited, prioritise the aerobic bottle.
- Optimal yield with ≥20 mL blood; minimum 5 mL per bottle.
- Label bottles clearly (do not cover barcodes) and send urgently to lab. Peel off miniature barcode for patient notes.
🎯 Special Situations
- Oncology/Haematology patients often have central venous catheters (CVCs) or ports – send one set via the line and one peripherally.
- Suspected infective endocarditis: take at least 3 sets from different sites/times before starting antibiotics.
- The more sets taken, the higher the diagnostic yield.
🧪 Results & Interpretation
- Preliminary results take ≥24 hours; full sensitivities take longer.
- Microbiology may call if a culture flags positive.
- False positives are common – always correlate with clinical picture. Discuss with Microbiology/ID team before acting.
👋 Practical Steps
- Wash hands and use PPE. Ensure name badge visible.
- Confirm patient identity, explain procedure, and obtain consent.
- Position patient comfortably, apply tourniquet, and identify vein (often antecubital fossa or forearm).
🧰 Equipment
- Sterile gloves & apron.
- Tourniquet.
- Chlorhexidine/alcohol wipes (repeat cleansing up to 5 times if needed).
- Needle & syringe OR vacutainer system.
- Aerobic & anaerobic culture bottles.
- Gauze/cotton wool, plaster, sharps bin.
💉 Technique
- Disinfect chosen site with chlorhexidine/alcohol, let dry fully. Do not re-touch.
- Insert needle (~30° angle), confirm flashback, and draw blood.
- Inoculate bottles (anaerobic first if using a syringe; aerobic first if using vacutainer).
- Release tourniquet before removing needle to reduce bruising.
- Apply pressure, achieve haemostasis, dress site, thank patient.
🧾 Finally
- Dispose of sharps safely.
- Label bottles at bedside with patient identifiers.
- Document time, site, and number of sets taken.
- Answer patient questions and provide reassurance.
⚠️ Complications & Pitfalls
- Failure: after 2–3 attempts, seek senior help or come back later.
- Haematoma: usually from not releasing tourniquet before removing needle.
- Arterial puncture: bright red pulsatile blood – withdraw and apply firm pressure.
- Contamination: the most frequent “complication.” Scrupulous skin prep is the best prevention.
📚 Teaching Pearls
- Draw before antibiotics unless delay is unsafe.
- Mark “time of collection” – helps interpret line vs peripheral sepsis.
- False positives waste resources; false negatives can be fatal – balance urgency with precision.
