Evaluation of indications for performing blood cultures in ICU patients: a pilot study

Introduction

Blood cultures are considered the golden standard in the diagnosis of this disease entity, with fever being the most common reason for culturing blood. The aim of this study was to evaluate the relative value of potential indications for performing blood cultures in ICU patients.

Methods

A prospective interventional pilot study. A new validated and reliable protocol including an extended list of indications for sampling blood for culture was developed and introduced at the ICU of a university hospital (July–October 2006). Culturing 'after physicians' request' was retained as an indication to cover all other possible signs suggestive for a beginning sepsis that were not included in the protocol, and to keep it manageable. Educational sessions for the staff were organized to draw attention to the indications, and for a procedure to follow when performing blood cultures. Indications were recorded in an electronic ICU data management system and linked to the results of the microbiological laboratory.

Results

During the 4-month period, 444 blood cultures were sampled from 180 patients (57.8 ± 15.0 years) of which 66.2% were male. Of these, 79 cultures yielded a microorganism; however, after correction for contaminants (n = 31), 48 cultures (10.8%) were considered a true bloodstream infection. Fever was found the most common reason for culturing (56.8%), followed by physicians' request (15.1%), and central venous catheter change after secondary transfer (10.6%), respectively. Coagulase-negative staphylococci (n = 12), Escherichia coli (n = 9), and Staphylococcus aureus (n = 8) were isolated most frequently. Of cultures sampled because of fever, 9.2% led to the diagnosis of true bacteremia, whereas this number increased up to 35.0% and 25.0% in cases where cultures were sampled because of hypotension or unexplained altered mental status. When blood was drawn because of the simultaneous presence of different indications, in the combinations 'hypotension and fever', 'hypotension and central venous catheter change', and 'hypotension and altered mental status', the culture yielded the causative pathogen in 33.3% (n = 9), 60.0% (n = 5), and 75.0% (n = 4), which was statistically significant when compared with the other indications (all P < 0.01). The monocentric setting and the small sample size concerns the major limitations of this pilot study.

Conclusion

Beside fever, other indications suggestive for systemic infection should be considered for blood culturing in ICU patients. However, further evaluation is needed to confirm these preliminary findings.