When do you repeat blood culture in a patient with suspected bacteremia or sepsis?

From the Guidelines

Blood cultures should not be repeated routinely in patients with suspected bacteremia or sepsis, but rather in specific situations where clinical suspicion of continuous or recurrent bacteremia or fungemia exists, or for test of cure, 48–96 hours after initiation of appropriate therapy for bacteremia/fungemia. The decision to repeat blood cultures should be guided by clinical judgment, taking into account the patient's response to antimicrobial therapy, the presence of persistent fever or instability, and the need to monitor clearance of certain pathogens 1.

Indications for Repeat Blood Cultures

• When a patient remains febrile or clinically unstable after 48-72 hours of appropriate antimicrobial therapy
• When monitoring clearance of certain pathogens like Staphylococcus aureus or fungal infections
• When endocarditis is suspected
• When there's a need to document bloodstream clearance before removing central venous catheters or completing antibiotic therapy

Recommendations for Obtaining Blood Cultures

• Obtain two to four blood cultures within the first 24 hours of the onset of fever, before the initiation of antimicrobial therapy, if possible 1
• Additional blood cultures should be drawn thereafter only when there is clinical suspicion of continuing or recurrent bacteremia or fungemia, or for test of cure, 48–96 hours after initiation of appropriate therapy for bacteremia/fungemia 1
• For patients without an indwelling vascular catheter, obtain at least two blood cultures using strict aseptic technique from peripheral sites by separate venipunctures after appropriate disinfection of the skin 1

Rationale for Selective Repeat Cultures

• Most bacteremia clears within 24-48 hours of appropriate therapy
• Routine repeat cultures have low yield, increase costs, and may lead to false positives
• Repeated blood draws can contribute to anemia and potentially increase the risk of contamination 1

From the Research

Repeating Blood Culture in Suspected Bacteremia or Sepsis

• The decision to repeat blood culture in a patient with suspected bacteremia or sepsis depends on various factors, including the clinical presentation, initial blood culture results, and the presence of any potential sources of infection 2.
• If the initial blood cultures are negative, it is generally recommended to wait for 48-72 hours before repeating the blood culture, as the probability of bacteremia is low after 24 hours of negative cultures 3.
• However, in certain cases, such as endovascular infections or when prompt initiation of antibiotics is needed prior to obtaining primary source cultures, routine blood cultures may be recommended 2.
• The time to positivity of blood cultures can also support early re-evaluation of empiric broad-spectrum antimicrobial therapy, with a median time to positivity of 15.7 hours in one study 3.
• It is essential to consider the clinical context and potential risks associated with empiric antibiotic treatment, as well as the implications of improper blood culture collection technique leading to false positive results 4.
• In cases where blood cultures are low-yield, blood cultures can be considered for patients at risk of adverse events if a bacteremia is missed, such as patients with pacemakers and severe purulent cellulitis 2.
• For patients with adequate source control and no risk factors or concern for endovascular infection, most streptococci or Enterobacterales bacteremias do not require routine follow-up blood cultures 2.
• The use of rapid diagnostic technology and antibiotic stewardship programs can help limit antibiotic courses among patients with negative cultures, and antibiotic de-escalation in culture-negative sepsis is both recommended and feasible in patients showing clinical signs of improvement 5.