Utilization and diagnostic yield of blood cultures in a surgical intensive care unit

Objective: To evaluate the diagnostic yield of blood cultures obtained in a surgical intensive care unit (ICU) and to assess factors potentially influencing yield. Design: Retrospective, descriptive study. Setting: Surgical ICU in a university hospital. Subjects: All patients who had a blood culture obtained during their admission to the trauma/neurosurgical ICU of Presbyterian University Hospital from January 1, 1993 to December 31, 1993. Measurements and Main Results: Blood culture isolates were categorized as pathogens or contaminants and overall diagnostic yield was determined, Blood cultures were positive for pathogens in 4.6% of all culture episodes, while contaminants were isolated in 5.5% of all culture episodes. A total of 23 true bacteremias were identified in 21 patients, for an overall rate of bacteremia of 3.6 per 100 admissions (5.9 per 1,000 patient days). Concurrent antibiotics were being used at the time of blood culture in 65.3% of all culture episodes. The yield for pathogens was significantly lower (2.2%) when cultures were obtained on antibiotics compared with culture episodes obtained off antibiotics (6.4%) (p < .05). Single set blood culture episodes were obtained in similar to 32% of all culturing episodes with the overall yield for pathogens of these culturing episodes lower (2.9%) than that of multiple set culture episodes (5.3%) (p = NS). Conclusions: Blood culture yield in this surgical ICU was relatively low in comparison with other published studies. The data further suggest that concurrent use of systemic antibiotics and inappropriate or excessive culturing may negatively influence blood culture yield.