Best Clinical Practice: Blood Culture Utility in the Emergency Department

Brit Long, MD; Alex Koyfman, MD

Disclosures

J Emerg Med. 2016;51(5):529-539. 

In This Article

Abstract and Introduction

Abstract

Background: Bacteremia affects 200,000 patients per year, with the potential for significant morbidity and mortality. Blood cultures are considered the most sensitive method for detecting bacteremia and are commonly obtained in patients with fever, chills, leukocytosis, focal infections, and sepsis.

Objective: We sought to provide emergency physicians with a review of the literature concerning blood cultures in the emergency department.

Discussion: The utility of blood cultures has been a focus of controversy, prompting research evaluating effects on patient management. Bacteremia is associated with increased mortality, and blood cultures are often obtained for suspected infection. False-positive blood cultures are associated with harm, including increased duration of stay and cost. This review suggests that blood cultures are not recommended for patients with cellulitis, simple pyelonephritis, and community-acquired pneumonia, because the chance of a false-positive culture is greater than the prevalence of true positive cultures. Blood cultures are recommended for patients with sepsis, meningitis, complicated pyelonephritis, endocarditis, and health care–associated pneumonia. Clinical prediction rules that predict true positive cultures may prove useful. The clinical picture should take precedence. If cultures are obtained, two bottles of ≥7 mL should be obtained from separate peripheral sites.

Conclusions: Blood cultures are commonly obtained but demonstrate low yield in cellulitis, simple pyelonephritis, and community-acquired pneumonia. The Shapiro decision rule for predicting true bacteremia does show promise, but clinical gestalt should take precedence. To maximize utility, blood cultures should be obtained before antibiotic therapy begins. At least two blood cultures should be obtained from separate peripheral sites.

Introduction

Approximately 200,000 patients are affected by bacteremia per year, with 10 cases per 1000 hospital admissions.[1–4] True blood stream infections can cause significant mortality, ranging from 14% to 37%, with the upper range of mortality seen in intensive care unit (ICU) settings.[1,4,5] Blood stream infections, or bacteremia, generally result from endocarditis, an infected central venous catheter, primary bacteremia, pneumonia, severe abscess, osteomyelitis, cellulitis, intra-abdominal infection, and urinary tract infections.[1–3,6] Bacteremia does have high mortality, and because of the dangers of undertreatment, many physicians order cultures liberally.

Blood cultures are generally considered to be the most sensitive method for the detection of bacteremia and are thought to be useful in certain diagnoses and critically ill patients.[1,2,6] These cultures are commonly obtained in patients with fever, chills, leukocytosis, focal infections, sepsis, or suspected endocarditis. In the emergency department (ED), blood cultures are often ordered for patients with suspected infection, but the literature has questioned the utility of these cultures. Many guidelines do not state when blood cultures should be obtained, though the Infectious Disease Society of America (IDSA) provides recommendations for culture collection in several infections.[7–13] Obtaining blood cultures over the past decade has been tied to core measures and payments, introduced by the Joint Commission on Accreditation of Healthcare Organizations (JCAHO) and Centers for Medicaid and Medicare Services (CMS).[14–16]

Bacteremia is defined by a true-positive blood culture and, as discussed, is associated with mortality. However, half of these cultures are actually contaminants.[6,17] Organisms that are inoculated into culture bottles at the time of blood culture collection result in contamination. Only 4% to 7% of cultures are truly positive, and the false-positive blood cultures are not without potential risk and harm.[4,6,18,19]

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