September 17, 2019
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Study: Obtain blood culture before initiating antimicrobial therapy in sepsis

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Among patients with severe manifestations of sepsis, the sensitivity of blood cultures decreased after initiation of empirical antimicrobial therapy, according to a study published in the Annals of Internal Medicine.

“This is a constant debate in the medical field. Emergency medicine physicians want to administer antibiotics as soon as possible because it prevents mortality, whereas internal medicine physicians want two sets of blood cultures before antibiotics are administered so they can more reliably diagnose the organism,” Murtaza Akhter, MD, an assistant professor in the department of emergency medicine at the University of Arizona College of Medicine – Phoenix and attending physician at Maricopa Health System, said in a press release.

In the study, which was conducted at seven EDs in North America, Akhter and colleagues collected blood cultures before and within 120 minutes after initiation of antimicrobial treatment from adults with severe manifestations of sepsis, including systolic blood pressure less than 90 mm Hg or a serum lactate level of 4 mmol/L or more. A total of 325 patients (mean age, 65.6 years; 62.8% men) were included in the study.

The researchers found that blood cultures obtained before antimicrobial treatment were positive for at least one microbial pathogen in 31.4% of all patients, whereas blood cultures obtained after initiation of treatment were positive for at least one microbial pathogen in 19.4% of all patients (absolute difference, 12 percentage points; P < .001).

Among patients with severe manifestations of sepsis, the sensitivity of blood cultures decreased after initiation of empirical antimicrobial therapy, according to a study published in the Annals of Internal Medicine.
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Analyses also showed that the sensitivity of blood cultures obtained after initiation of antimicrobial therapy was 52.9% (95% CI, 42.8-62.9). When cultures from other anatomical sites obtained before and after administration of antimicrobial therapy were combined with cultures taken after initiation of therapy, the overall sensitivity was 67.6% (95% CI, 57.7-76.6).

“It was unknown how quickly blood cultures lose their ability to grow organisms after antibiotic administration. Now we know that even if blood cultures are performed very rapidly after antibiotics, they lose a significant amount of their diagnostic ability,” Akhter said. “Although administering antibiotics to septic patients is important, it is imperative to get at least one blood culture before providing treatment.”

The most commonly administered antimicrobial agents included beta-lactams, such as piperacillin-tazobactam (60.6%), third-generation cephalosporins (23.4%) and carbapenems (4.6%). Although protocol required cultures to be drawn within 120 minutes of treatment, the time frame was extended to 240 minutes due to difficulties in obtaining repeat blood cultures in 120 minutes.

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In an accompanying editorial, Jacqueline H. Geer, MD, and Mark D. Siegel, MD, both from Yale School of Medicine in New Haven, Connecticut, noted that these findings support the existing guidelines. However, they also emphasized the importance of timely treatment.

“While acknowledging the diagnostic value of obtaining blood cultures before antimicrobial agents are administered, it is crucial to prevent unintentional treatment delays, particularly given the increased risk for death associated with delaying anti-infective treatment. In contrast to other, more time-consuming procedures done to obtain cultures, such as lumbar puncture, blood cultures can generally be obtained in a few minutes, assuming standard equipment and qualified personnel are available. However, despite their simplicity, delays in obtaining blood cultures have been well documented, although the reasons for the delay are unclear. Future studies should explore methods to ensure that blood is drawn expeditiously, without imposing treatment delays,” they wrote. – by Melissa Foster

Disclosures: Akhter reports he received grants from the Maricopa Medical Foundation. Please see the study for all other authors’ relevant financial disclosures. Geer reports no relevant financial disclosures. Siegel reports he receives royalties from UpToDate and he has served as an expert witness in medical malpractice cases, some of which pertain to sepsis.