College of American Pathologists

  QT2 - Blood Culture Contamination




Updated October 12, 2005

Blood Culture Contamination QT2
Despite advancements in blood culture practices and technology, false-positive blood culture results due to contaminants continue to be a critical problem. The blood culture contamination rate is associated with increased length of hospital stay, additional expense, and the administration of unnecessary antibiotics. The blood culture contamination rate is the primary indicator of preanalytical performance in microbiology. The CAP requires you to monitor and evaluate key indicators of quality for improvement opportunities. Use of this monitor can help you meet this requirement.

Monitor Objective
Determine the rate of blood culture contamination using standardized criteria for classifying contaminants.

Data Collection
On a monthly basis, participants will tabulate the total number of blood cultures processed and the total number of contaminated blood cultures. For the purposes of this study, participants will consider a blood culture to be contaminated if one or more of the following organisms are found in only one of a series of blood culture specimens: Coagulase-negative Staphylococcus; Micrococcus; Alpha-hemolytic (viridans) streptococci; Propionibacterium acnes; Corynebacterium sp. (diptheroids); or Bacillus sp. Optional institution-specific subgroups may be used to track parameters that may affect contamination rates. This monitor includes only positive cultures identified by routine procedures used in the laboratory for detecting most microorganisms in blood specimens and excludes autopsy cultures. Additionally, neonatal totals can be tabulated separately from other blood cultures.

Performance Indicators

  • Total Contamination Rate (%)
  • Neonatal Contamination Rate (%)
  • Other Contamination Rate (%)

Input forms for quarterly data will be sent to participants approximately three weeks prior to the quarter.


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