Poor sensitivity for blood cultures drawn after antibiotics


Background: Early antibiotic administration reduces mortality in patients with severe sepsis. Administering antibiotics before blood cultures could potentially decrease time to treatment and improve outcomes, but the diagnostic yield of blood cultures drawn shortly after antibiotics is unknown.

Dr. Emily Waner

Study design: Prospective, patient-level, pre- and post-study.

Setting: Multicenter study in USA & Canada.

Synopsis: During 2013-2018, 330 adult patients were recruited from seven urban EDs. Patients with severe manifestations of sepsis (spontaneous bacterial peritonitis [SBP] less than 90 mm Hg and lactic acid of 4 or more) had blood cultures drawn before and after empiric antibiotic administration. Blood cultures were positive for one or more microbial pathogens in 31.4% of patients when drawn before antibiotics and in 19.4% of patients when drawn after antibiotics (absolute difference of 12.0% (95% confidence interval, 5.4%-18.6%; P less than .001). The sensitivity of blood cultures after antibiotic administration was 52.9% (95% CI, 43%-63%).

There were several study limitations including: lack of sequential recruitment, lower than expected proportion of bacteremic patients, and variation in blood culture collection. Despite this, the magnitude of the findings are convincing and support current practice.

Bottom line: Continue to obtain blood cultures before antibiotics.

Citation: Cheng MP et al. Blood culture results before and after antimicrobial administration in patients with severe manifestations of sepsis. Ann Intern Med. 2019 Oct 15;171(8):547-54.

Dr. Waner is clinical instructor of medicine, hospital medicine, at the Rocky Mountain Veterans Affairs Regional Medical Center, Aurora, Colo.

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