Low Rate of Clinical Consequences Derived from Results of Blood Cultures Obtained in an Internal Medicine Emergency Department

Abstract

Blood cultures detect bacteremia in individual patients and help define local pathogen and resistance spectra. At the same time, the benefits of blood culture results in the management of individual patients -- and therefore their cost-effectiveness -- are disputed. During 1 calendar year, we conducted a prospective study of emergency department admissions with blood culture draws and at least a 3-day hospitalization afterwards. We prospectively surveyed treating physicians on usefulness of blood culture results for patient management. 428 diagnostic episodes (emergency visits) involving 390 patients occurred during the study period from 10/2002 to 10/2003. The analysis included 188/428 (44%) episodes with blood culture draws performed according to the predefined clinical standard where patients were hospitalized with sufficient duration. Absence of therapeutic consequences in response to blood culture results was reported for 138/142 (97%) of episodes with negative blood culture results, for 16/21 (76%) with blood culture results positive only for skin flora, and for 14/25 (56%) of episodes with blood cultures positive for obligate pathogens. Treating physicians regarded the blood culture results necessary for clarifying the etiology in 34/188 (18%) episodes, and rated blood culture results necessary for their therapeutic decisions in 29/188 (15%) episodes. Negative blood culture results rarely changed the management of medical inpatients. Our study suggests that in settings with broad-spectrum empirical antibiotic therapy positive blood culture results for obligate pathogens trigger adjustment of the antibiotic therapy in only about half of instances. Many blood cultures drawn in the emergency department where considered unnecessary by ward physicians. Guidelines for preventing unnecessary blood culture draws are warranted in order to increase the rate of their meaningful clinical consequences for medical inpatients initially treated with broad-spectrum empirical antibiotics.