Are repeat blood cultures needed in a patient with sepsis and pending blood cultures from 48 hours prior?

Repeat Blood Cultures in Sepsis with Pending Cultures from 48 Hours Prior

Repeat blood cultures are not needed in a patient with sepsis who already has blood cultures pending from 48 hours prior, unless there is a clinical change or suspicion of a new source of infection.

Rationale for Not Repeating Blood Cultures

The Surviving Sepsis Campaign guidelines provide clear recommendations regarding blood cultures in sepsis management:

1. Blood cultures should be obtained before starting antimicrobial therapy in patients with suspected sepsis 1
2. Two or more sets of blood cultures (aerobic and anaerobic) are recommended before initiating antimicrobial therapy 1
3. Sterilization of cultures occurs rapidly (within minutes to hours) after the first dose of appropriate antimicrobials 1

When blood cultures are already pending from 48 hours prior, repeating them offers limited additional diagnostic value for several reasons:

• The original cultures should have been drawn before antimicrobial initiation, maximizing their yield
• Research shows significantly reduced sensitivity of blood cultures drawn after antimicrobial therapy has begun 2, 3
• A study by Cheng et al. demonstrated that the absolute difference in positive blood culture rates between pre-antimicrobial and post-antimicrobial samples was 12.0% (31.4% vs 19.4%), with post-antimicrobial culture sensitivity of only 52.9% 2

Exceptions When Repeat Cultures May Be Warranted

Despite the general recommendation against routine repeat cultures, there are specific clinical scenarios where repeat blood cultures may be indicated:

1. Clinical deterioration or lack of improvement despite appropriate antimicrobial therapy
2. Suspected new source of infection or secondary infection
3. Suspected catheter-related bloodstream infection - in this case, paired cultures from the catheter and periphery are recommended 1
4. Need to document clearance of bacteremia for certain pathogens like Staphylococcus aureus 4

Proper Blood Culture Technique When Required

If repeat blood cultures are clinically indicated, proper technique is essential:

• Clean skin with 70% isopropyl alcohol or chlorhexidine (>0.5%)
• Allow adequate drying time
• Use fresh venipuncture from a peripheral site
• Collect adequate volume (20-30 mL of blood per culture set)
• Prioritize the aerobic bottle if insufficient blood is available 4

Antimicrobial Stewardship Considerations

The decision about repeat cultures should be balanced with antimicrobial stewardship principles:

• Initial cultures are critical for pathogen identification and de-escalation of therapy
• De-escalation of antimicrobial therapy based on culture results is associated with less resistant organisms, fewer side effects, and lower costs 1
• Unnecessary repeat cultures can lead to inappropriate antimicrobial use 1

Common Pitfalls to Avoid

1. "Pan-culturing" without clinical indication - this practice should be discouraged as it can lead to inappropriate antimicrobial use 1
2. Delaying antimicrobial therapy to obtain cultures - if obtaining cultures would significantly delay treatment in a critically ill patient, antimicrobial therapy should take priority 1
3. Poor technique leading to contamination - proper skin preparation is essential to avoid false positives 4

In summary, for a patient with sepsis who already has blood cultures pending from 48 hours prior, repeat blood cultures are generally not indicated unless there is a specific clinical reason such as deterioration, suspected new infection source, or need to document clearance of specific pathogens.