Is it necessary to take blood cultures immediately when a patient presents with fever or chills, or does taking them after a period of time (delayed) not decrease sensitivity?

Blood Culture Collection Timing in Suspected Sepsis

Blood cultures should be taken as soon as possible after onset of fever or chills to maximize diagnostic yield. 1, 2

Optimal Timing for Blood Culture Collection

• Blood cultures should be obtained before initiating antimicrobial therapy if this can be done without substantial delay (ideally within 45 minutes) to prevent sterilization of cultures 1, 2
• The literature contains no clinical data showing that delayed blood culture collection improves sensitivity; expert opinion consistently recommends immediate collection following onset of fever 1
• Bacteria are rapidly cleared from blood, and fever typically develops 30-90 minutes after an episode of bacteremia, making prompt collection critical 1
• Contrary to some beliefs, timing blood cultures to coincide with temperature spikes has not been shown to improve yield 1, 3

Recommended Blood Culture Collection Protocol

• Obtain 3-4 blood cultures within the first 24 hours of fever onset 1
• Each blood culture should consist of 20-30 mL of blood drawn at a single time from a single site 1
• For patients without intravascular catheters, obtain at least two blood cultures from separate peripheral venipuncture sites 1
• For patients with intravascular catheters, draw one culture through venipuncture and at least one through the catheter 1
• Use proper skin antisepsis: 2% chlorhexidine gluconate in 70% isopropyl alcohol (preferred) or tincture of iodine, allowing 30 seconds drying time 1
• Label each culture with exact time, date, and anatomic site 1

Special Considerations

• Blood cultures can be drawn consecutively or simultaneously, except in cases of suspected endovascular infection, where timed intervals may be used to demonstrate continuous bacteremia 1
• The cumulative sensitivity increases with each additional culture: first culture detects approximately 73%, first two detect about 90%, and three cultures detect 96-98% of bloodstream infections 4
• Paired blood cultures provide more useful information than single blood cultures and help distinguish true pathogens from contaminants 1, 5

Common Pitfalls to Avoid

• Delaying antimicrobial therapy beyond 45 minutes to obtain blood cultures, as this may increase mortality 1, 2
• Collecting blood cultures through sites with compromised skin integrity (burns, dermatological conditions) or high contamination risk (femoral site) 1
• Obtaining blood cultures via peripherally inserted venous catheters at time of insertion due to high contamination rates 1
• "Pan-culturing" all possible sites without clinical indication, which can lead to inappropriate antimicrobial use 1

Conclusion

The evidence clearly supports collecting blood cultures as soon as possible after fever onset, rather than waiting. Bacteremia often precedes fever, and delaying collection does not improve sensitivity 3. The priority should be obtaining adequate blood volume from appropriate sites using proper technique, while ensuring antimicrobial therapy is not significantly delayed 1, 2.