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Diagnostic Decision
Blood Cultures
Abstract
We reviewed the literature on the performance of the blood culture as a diagnostic test and analyzed the data with Bayes' theorem to find the optimal number of cultures to draw. The blood culture is unusually dependent on physician behavior (use of sterile technique, the number and timing of cultures, volume of blood drawn) and on their clinical judgment (estimating the pretest probability of bacteremia, anticipating the causative pathogen, interpreting the results). Because there is no independent "gold-standard" procedure against which to evaluate this test, sensitivity and specificity can only be approximated. Sensitivity can be maximized by doing multiple cultures containing at least 10 mL of blood per set. Specificity can be maximized by adhering strictly to aseptic techniques and by requiring that multiple sets be positive for the series to be considered positive when the anticipated pathogens are also common contaminants. Two or three blood culture sets almost always suffice to establish or rule out bacteremia, although on some occasions obtaining more than three sets of cultures is indicated. One set is rarely, if ever, sufficient.
- bacteremia
- bacterial endocarditis
- Bayes' theorem
- blood culture
- culture media
- prosthetic valve endocarditis
- septicemia
Article and Author Information
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▸From the Division of General Medicine, the Charles A. Dana Research Institute, the Harvard Thorndike Laboratory of the Beth Israel Hospital, and the Harvard Medical School, Boston; and the Cambridge Hospital, Cambridge, Massachusetts.
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▸This paper was commissioned by the Blue Cross-Blue Shield Medical Necessity Project, under auspices of the Society for Research and Education in Primary Care Internal Medicine (SREPCIM), and is the 12th in a series being published in the Diagnosis and Treatment section. Harold C. Sox, Jr., M.D., is the editor for the series, and these papers are also being reviewed by John M. Eisenberg, M.D., and Sankey V. Williams, M.D., our consultants for Diagnostic Decision papers, as well as by selected manuscript consultants. This series will be published in a collective reprint, the availability of which will be announced later. The reprint will include the introductory article by Dr. Sox, which appeared on pages 60-66 in the January 1986 issue.—The Editor.
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▸Requests for reprints should be addressed to Mark Aronson, M.D.; Beth Israel Hospital, 330 Brookline Avenue; Boston, MA 02215.
- ©1987 American College of Physicians
