226. The Relationship between Positivity of Blood Culture and Blood Volume How Much Blood Is Enough?
Session: Poster Abstract Session: Diagnostic Microbiology
Thursday, October 3, 2013
Room: The Moscone Center: Poster Hall C
Posters
  • bv poster IDSAsdkk (2).pdf (372.4 kB)
  • Background:

    It is commonly accepted that a larger volumes of blood increase the yield of true positive cultures and optimally 20 ml should be obtained per culture set (2 bottles). The current CAP guideline state that laboratories should periodically monitor collected blood volumes and provide feedback to clinical staff. However, it also states that automated blood culture systems approved or cleared by the FDA may use smaller volumes per culture set and are acceptable.  It is currently unknown as to the minimum volume of blood that is acceptable for culture and for determining clinical significance.  The objective of this study was to determine the association between blood culture volume and rate of true positive blood cultures, and blood culture contaminants.

    Methods:

    The volume of blood from 3932 BD BACTEC Plus Aerobic/F negative bottles collected from patients in ICUs and acute care floors at 8 hospitals over 2 months (January and February 2013) was estimated automatically from blood background signal data in the BD BACTEC FX instrument. The volume were estimated based on average monthly volume from an individual ICU or acute care floor during the 2 month period (a total of 63 units) and correlated to growth of microorganisms using a Pearson product-moment correlation coefficient. Contaminated blood cultures were defined using established microbiology criteria and all other positive cultures were considered true positives.

    Results:

    A total of 562 blood cultures collected by unit/floor were positive (14.3%) with the average blood volume of 3.88 ml [SD 3.9]. 137 blood cultures were contaminants (3.5%) and there was no correlation between blood culture volume and blood culture contamination rate [r=-0.1, p=0.33).  There were 425 blood cultures that were determined to be true positives (10.8%) and there was no correlation between blood culture volume and rate of true blood culture positivity (r=0.07, p=0.60).

    Conclusion:

    No correlation was found between the blood volume obtained for blood cultures and percent of true positive cultures or contaminated cultures. Lower volumes of blood may provide adequate clinical information on the current microbiologic platforms commonly employed in the laboratory, but more comprehensive, larger studies are needed to further explore this association.

    Tal Mann, MD, Detroit Medical Center (DMC)/ Wayne State University, Detroit, MI, Vikram Desai, M.D., Wayne state university, Detroit, MI, Paul Lephart, PhD, Detroit Medical Center University Laboratories, Detroit, MI, Hossein Salimnia, PhD, Detroit Medical Center/Wayne State University, Detroit, MI, Robert Mitchell, MT/ASCP, DMC University Laboratories, Detroit, MI, Keith Kaye, MD, MPH, FIDSA, FSHEA, Infectious Diseases, Detroit Medical Center/ Wayne State University, Detroit, MI and Sorabh Dhar, MD, Detroit Medical Center (DMC) / Wayne State University, Detroit, MI

    Disclosures:

    T. Mann, None

    V. Desai, None

    P. Lephart, None

    H. Salimnia, None

    R. Mitchell, None

    K. Kaye, None

    S. Dhar, None

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