When should blood cultures be repeated in a patient with sepsis (Systemic Inflammatory Response Syndrome) who is not responding to antibiotic therapy?

From the Guidelines

Blood cultures should be repeated in a patient with sepsis who is not responding to antibiotic therapy after 48-72 hours of treatment, or sooner if there is clinical deterioration such as new or persistent fever, worsening hemodynamic instability, or progression of organ dysfunction. This recommendation is based on the most recent and highest quality study available, which emphasizes the importance of obtaining appropriate cultures before antimicrobial therapy is initiated if such cultures do not cause significant delay 1.

Key Considerations for Repeating Blood Cultures

• Additional blood cultures should be collected before making any changes to the antibiotic regimen, as this helps determine whether the current infection is persistent or if a new pathogen has emerged.
• Two sets of blood cultures (each set consisting of one aerobic and one anaerobic bottle) should be drawn from different venipuncture sites, with at least 10mL of blood per bottle to maximize yield.
• Timing the collection just before or during a fever spike can increase the chance of pathogen detection.
• Repeating cultures is crucial because it guides appropriate antibiotic adjustments, identifies potential antibiotic resistance, and helps detect complications like endocarditis or metastatic infections that may require surgical intervention.

Special Considerations for Catheter-Related Bloodstream Infections

• In cases of suspected catheter-related bloodstream infections, paired blood cultures (one from the catheter and one from a peripheral site) should be obtained to determine if the catheter needs removal.
• The decision to remove the catheter should be based on the results of the blood cultures and clinical judgment, as the presence of a catheter-related infection can significantly impact patient outcomes 1.

Importance of Timely Culture Collection

• Obtaining cultures prior to the administration of antimicrobials significantly increases the yield of cultures, making identification of a pathogen more likely 1.
• The risk/benefit ratio favors rapid administration of antimicrobials if it is not logistically possible to obtain cultures promptly, but cultures should be obtained as soon as possible to guide antibiotic therapy 1.

From the Research

Blood Culture Repeat in Sepsis

• The decision to repeat blood cultures in a patient with sepsis who is not responding to antibiotic therapy should be based on clinical judgment and the individual patient's circumstances 2.
• Repeating blood cultures can help identify persistent bacteremia or the development of new infections, but it may not always be necessary or useful 3.
• The sensitivity of blood cultures obtained after initiation of antimicrobial therapy is lower than that of pre-antimicrobial blood cultures, with a sensitivity of 52.9% 2.
• Factors to consider when deciding whether to repeat blood cultures include the patient's clinical response to treatment, the presence of persistent fever or instability, and the risk of antibiotic resistance 4, 5, 6.

Timing of Blood Culture Repeat

• There is no specific guideline on the optimal timing of repeating blood cultures in patients with sepsis, but it is generally recommended to repeat cultures if there is a change in the patient's clinical condition or if the initial cultures are negative 2.
• Repeating blood cultures within 120 minutes after initiation of antimicrobial therapy may not be useful, as the sensitivity of the cultures is lower during this time period 2.
• The decision to repeat blood cultures should be individualized and based on the patient's specific circumstances, rather than following a rigid protocol 4, 6.

Clinical Considerations

• Patients with sepsis who are not responding to antibiotic therapy should be carefully evaluated for potential causes of treatment failure, including antibiotic resistance, inadequate source control, and underlying conditions that may be contributing to the infection 4, 5, 6.
• Repeating blood cultures can be useful in identifying persistent bacteremia or the development of new infections, but it should be done in conjunction with other diagnostic tests and clinical evaluations 3, 2.
• The use of biomarkers, such as procalcitonin, may help guide antibiotic therapy and reduce the need for repeated blood cultures 5.