Study supports taking blood cultures before beginning treatment for sepsis

Sept. 20, 2019

Severe bacterial infections are a leading cause of death globally. Delays in effective treatment can increase the chance that a patient dies but treating a patient before blood cultures are drawn may make it impossible to identify the bacteria causing the infection and make it challenging to identify the best choice of treatment. Current clinical guidelines recommend that blood cultures be drawn before treatment begins, but no previous studies have definitively compared drawing a blood culture shortly after a patient begins antimicrobial treatment with drawing blood cultures prior to treatment. In a new study led by investigators from Brigham and Women's Hospital, a team performed a prospective study in seven centers across North America and found that blood cultures drawn after antimicrobial administration resulted in a loss of almost 50 percent of available clinical information. The team reports these findings, which provide a basis for clinical guidelines for the care of patients with sepsis, in Annals of Internal Medicine.

"These findings are important in considering the optimal balance between prompt antimicrobial administration and the need for accurate microbiological data in the care of patients with sepsis," said corresponding author Matthew Cheng, MD, a clinical instructor in the Brigham's Division of Infectious Diseases. "Given the global burden of sepsis, deepening our understanding of how best to treat this condition is critically important."

Cheng and colleagues conducted a study known as FABLED (eFfect of Antimicrobial administration on BLood culture positivity in patients with severe manifestations of sepsis in the Emergency Department), a patient-level, single-group, diagnostic study. Between November 2013 and September 2018, the team enrolled adult patients who presented to the emergency department with severe manifestations of sepsis. Each patient had two blood cultures drawn before treatment initiation and repeat blood cultures drawn within two hours after starting treatment.

Pre-treatment blood cultures were positive for one or more microbial pathogens in 102-of-325 (31.4 percent) patients. After-treatment blood cultures were positive for one or more microbial pathogens in 63-of-325 (19.4 percent) patients. The sensitivity of post-treatment cultures, or percentage of samples accurately identified as having the same pathogens pre-treatment, was 52.9 percent.

Patients with sepsis are generally treated initially with a broad-spectrum antibiotic, but Cheng and colleagues note the importance of identifying the right narrow-spectrum antibiotic based on a patient's blood culture. Without an accurate picture of the microbial landscape prior to initiating treatment, it may be extremely challenging for physicians to select the right antibiotic.

"When it comes to treating sepsis safely and effectively, microbiological diagnosis is key," said Cheng. "Despite the importance of starting treatment early for sepsis patients, our results support the Surviving Sepsis Campaign guidelines and suggest that blood cultures should not be routinely deferred."

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