Blood Cultures In Community Acquired Pneumonia


Author: William Ford, MD (EM Resident Physician, PGY-2, NUEM) // Edited by: Michael Macias, MD (EM Resident Physician, PGY-4, NUEM) // Expert Commentary: Brian Wolf, MD

Citation: [Peer-Reviewed, Web Publication] Ford W , Macias M (2016, November 1). Blood Cultures In Community Acquired Pneumonia [NUEM Blog. Expert Commentary By Wolf B]. Retrieved from

Since the announcement of the JCAHO/CMS core measure for community acquired pneumonia in 2002, emergency departments nationwide have shifted towards obtaining cultures for increasing numbers of patients who present with community acquired pneumonia.  This trend has persisted despite revisions in the guidelines in 2005 and 2007, which advocated for a more restrictive use of blood cultures than previously described [1].  In such a way, the reflex of obtaining blood cultures before the initiation of antibiotics has pervaded the practice of medicine; however, this practice may not necessarily be evidence-based. 

In the setting of uncomplicated community acquired pneumonia, blood cultures have a relatively low overall yield of approximately 6-9%.  Antibiotic selection in community acquired pneumonia rarely deviates from standard empiric therapy as a result of blood cultures, with broadening of antibiotics in only 0.5-1.0% of cases, including those that were admitted to the intensive care unit.  Of these scarce cases, three-quarters of the changes were in patients who came from nursing homes without proper antibiotic therapy [2,3].

For such little gain, the healthcare cost of obtaining blood cultures includes the price of the lab tests—$203 for blood culture, $62 for gram stain, $52 for identification, $249 for susceptibility—and is additionally associated with an increased length of hospital stay of 4.5 days, increased lab charges of 20%, and increased antibiotic charges of 39% [4].  While the provider may not think twice of these numbers, they are not likely to go unnoticed by the patient.

As a result, blood cultures in community acquired pneumonia are no longer a CMS quality measure.  Guidelines now recommend cultures for pneumonia in circumstances including severe community acquired, healthcare-acquired pneumonia, cirrhosis, asplenia, or concern for cavitary lesions, empyema, or neutropenia [5].  More judicious use of blood cultures will result in an overall improved utility of the test and hospital resources being used more effectively elsewhere.

Expert Commentary

Wonderful job addressing the issue of unnecessary blood cultures in patients admitted with uncomplicated community acquired pneumonia (CAP). Current IDSA guidelines only recommend blood cultures in patients admitted with either severe CAP, certain radiographic findings, or those with predisposing risk factors for bacteremia [6]. Severe CAP in many studies is defined by a patient requiring ICU admission for hypotension or profound hypoxia. In a study by Paganin et al. patients admitted to the ICU for severe CAP had positive blood cultures 33% of the time compared to the 6-9% stated in your post [7]. Unpublished data from Northwestern on the utility of blood cultures in uncomplicated CAP identified 2 positive cultures out of 308 samplesover a 6 month period, of which only 1 of the 2 cultures represented a true positive. Patients with cavitary lesions or pleural effusions may also benefit from blood cultures in the hopes of isolating the provoking organism. 

Risk factors predisposing patients to bacteremia with CAP are similar to those that cause bacteremia in general. These include functional/anatomical asplenia, chronic severe cirrhosis, leukopenia, and alcoholism [8]. However, if a patient has uncomplicated CAP without these risk factors, then the utility of blood cultures becomes fairly minimal. As outlined by your review, false positive blood cultures can lead to unnecessary additional testing and prolonged hospital stay. With fevers being a common symptom in those with pneumonia, reflexively ordering blood cultures is an easy habit to get into. New habits need to be established by clinicians to help relieve the financial strain of over ordering blood cultures on the healthcare system.

Brian Wolf, MD
Fellow, Division of Infectious Disease; Department of Medicine; Northwestern University, Feinberg School of Medicine

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  1. Makam A,  Auerbach A, Steinman M. Blood Culture Use in the Emergency Department in Patients Hospitalized for Community-Acquired Pneumonia. JAMA Intern Med. 2014;174(5):803-806.
  2. Campbell S, et al. The Contribution of Blood Cultures to the Clinical Management of Adult Patients Admitted to the Hospital with Community-Acquired Pneumonia:  A Prospective Observational Study. CHEST Journal. 123.4 (2003): 1142-1150.
  3. Kennedy M, et al. Do emergency department blood cultures change practice in patients with pneumonia? Annals of emergency medicine 46.5 (2005): 393-400.
  4. Hall K, Lyman J. Updated review of blood culture contamination. Clinical microbiology reviews 19.4 (2006): 788-802.
  5. Wunderink RG, Waterer GW. Community Acquired Pneumonia. N Engl J Med 2014; 370:543-551.
  6. Mandell, Lionel A., Richard G. Wunderink, et al. Infectious Diseases Society of America/American Thoracic Society Consensus Guidelines on the Management of Community-Acquired Pneumonia in Adults. CID 2007; 44:27-72.
  7. Paganin F, Lilienthal F, Bourdin A, et al. Severe community-acquired pneumonia: assessment of microbial aetiology as mortality factor. Eur Respir J 2004;24:779–85. 
  8. Ruiz M, Ewig S, Torres A, et al. Severe community-acquired pneu- monia. Am J Respir Crit Care Med 1999; 160:923. 
Posted on October 31, 2016 and filed under Infectious Disease.