Should blood cultures be obtained in patients with suspected bacteremia or sepsis?

Blood Culture Collection in Suspected Bacteremia or Sepsis

Blood cultures should be obtained before starting antimicrobial therapy in all patients with suspected sepsis or bacteremia, as long as collection does not substantially delay (>45 minutes) the administration of antibiotics.1

Indications for Blood Cultures

Blood cultures should be collected when there are specific clinical indicators of possible bacteremia:

• Fever (especially new onset) or chills
• Hypothermia
• Leukocytosis or left-shift of neutrophils
• Neutropenia
• Suspected infection with hypoalbuminemia
• Development of renal failure
• Signs of hemodynamic compromise 1
• Suspected sepsis or septic shock 1

Proper Collection Technique

When obtaining blood cultures:

• Collect at least two sets (aerobic and anaerobic bottles) before initiating antimicrobial therapy 1, 2
• Obtain 20-30 mL of blood per culture (10-30 mL per bottle) 1, 2
• Use strict aseptic technique:
  • Swab skin twice with 70% isopropyl alcohol or iodine-containing solution 1
  • Sterilize the blood culture bottle stopper prior to inoculation 1
  • Use 2% chlorhexidine in 70% isopropyl alcohol for skin preparation 2
• Collect via fresh venipuncture from separate peripheral sites 1
• Avoid sites associated with skin contamination (e.g., femoral) or loss of skin integrity 1
• Change the needle used for venipuncture prior to inoculating blood into culture bottles 1

Timing Considerations

• Collect blood cultures as soon as possible after onset of fever or chills 1, 2
• If obtaining cultures would delay antimicrobial therapy by more than 45 minutes, prioritize starting antibiotics 1
• The diagnostic yield significantly decreases when blood cultures are collected after antibiotic administration has begun 3

Special Situations

Intravascular Catheters

• For patients with intravascular catheters (in place >48 hours) where catheter-associated infection is suspected:
  • Obtain at least one blood culture set from the catheter
  • Collect simultaneous peripheral blood cultures 1

Patients Already on Antibiotics

• If cultures must be obtained while on antibiotics, use media with antibiotic-absorbing substances (BacT/Alert FAN and BACTEC Plus/F) 1, 2
• Be aware that antibiotic therapy before sampling significantly reduces pathogen detection (50.6% positivity without antibiotics vs. 27.7% with antibiotics) 3

Avoiding Common Pitfalls

1. Delayed antibiotic administration: While obtaining cultures before antibiotics is ideal, never delay antimicrobial therapy by more than 45 minutes to obtain cultures in critically ill patients 1

2. Insufficient blood volume: Ensure adequate volume (20-30 mL per culture) as this significantly impacts detection rates 1, 2

3. "Pan-culturing": Avoid indiscriminate culturing of all potential sites without clinical indication, as this leads to inappropriate antimicrobial use 1

4. Single blood cultures: Always obtain paired cultures for better diagnostic yield 2

5. Poor technique: Improper skin preparation leads to contamination and false positives 1

Blood cultures remain a critical diagnostic tool in suspected bacteremia and sepsis, with proper collection technique and timing being essential for maximizing their utility while minimizing false results that could lead to inappropriate antimicrobial therapy.