How often should blood cultures be repeated in patients with suspected bloodstream infections?

From the Guidelines

Blood cultures should not be routinely repeated in patients with suspected bloodstream infections unless there are specific clinical indications, such as persistent fever or clinical instability after 48-72 hours of appropriate antimicrobial therapy, suspicion of a new infection, or to document clearance of bacteremia in certain infections. When repeat cultures are necessary, the frequency should be guided by the patient's clinical status and the identified pathogen, if known. For example, in cases of endocarditis, cultures every 24-48 hours until sterilization is confirmed may be appropriate 1. The decision to repeat cultures should be based on clinical judgment rather than a fixed schedule, taking into account the potential risks of false positives, unnecessary antibiotic use, and patient discomfort.

Some key considerations for obtaining blood cultures include:

• Drawing initial cultures from different sites before starting antibiotics
• Using strict aseptic technique and appropriate skin disinfection
• Obtaining at least two blood cultures using separate venipunctures
• Labeling the blood culture with the exact time, date, and anatomic site from which it was taken
• Drawing 20-30 mL of blood per culture

It is also important to note that the timing of blood culture orders should be dictated by patient acuity, and that contaminated blood culture bottles are common and can be costly to the healthcare system 1. Therefore, meticulous care should be taken in skin preparation prior to venipuncture, and the use of iodine tincture, chlorine peroxide, and chlorhexidine gluconate (CHG) as skin disinfectants is recommended 1.

In general, the approach to repeating blood cultures should be individualized based on the patient's specific clinical situation, and should take into account the latest evidence-based guidelines and recommendations 1.

From the Research

Frequency of Repeating Blood Cultures

• The frequency of repeating blood cultures in patients with suspected bloodstream infections varies depending on the clinical context and guidelines.
• A study published in the European Heart Journal in 2013 2 found that persistent positive blood cultures after 48-72 hours of antibiotic therapy were associated with a worse prognosis in patients with left-sided infective endocarditis.
• Another study published in Clinical Infectious Diseases in 2017 3 found that follow-up blood cultures in gram-negative bacteremia added little value in the management of the infection, and that unrestrained use of blood cultures can have serious implications for patients.

Timing of Repeating Blood Cultures

• A study published in the Annals of Pharmacotherapy in 2014 4 found that 98% of aerobic gram-positive and gram-negative bloodstream infections were detected within 48 hours of culture incubation, and that clinicians may adjust empirical antibiotic coverage at this time with little risk for subsequent bacterial pathogen detection.
• A study published in Clinical Microbiology and Infection in 2004 5 found that repeating blood cultures during hospital stay was a common practice, but that the yield was low, and that guidelines for repeating blood cultures may decrease unnecessary testing.

Special Populations

• A study published in Pediatric Blood and Cancer in 2013 6 found that in pediatric oncology patients with febrile neutropenia, bacteremia was detected nearly twice as frequently in initial blood cultures than in repeat blood cultures obtained when the initial blood culture was negative.
• The same study found that the risk of detecting bacteremia in repeat blood cultures was higher in patients with a previous history of bacteremia or hospitalized for more than 48 hours prior to the onset of fever.

Clinical Implications

• The decision to repeat blood cultures should be based on clinical judgment and guidelines, taking into account the patient's clinical context and risk factors for bloodstream infections.
• Repeating blood cultures too frequently can lead to unnecessary testing, increased healthcare costs, and prolonged hospital stays, as noted in the study published in Clinical Infectious Diseases in 2017 3.