Turning up the volume on suboptimal blood culture collection practices

Ms. Angela Hills1, Mrs Mercedes Ray1, Dr Jacqueline Harper2, A/Prof Jaimi Greenslade1,3, Dr. James Hughes1,3, Dr Julian  Williams1,4

1Royal Brisbane and Women’s Hospital, Herston, Australia, 2Pathology Queensland, Herston, Australia, 3Queensland University of Technology, Kelvin Grove, Australia, 4University of Queensland, St Lucia, Australia

Background: Blood cultures (BC) are one of the most common pathology tests ordered in the emergency department (ED). Quality of BC collection may be quantified through contamination rates, the number of sets per patient and the volume of blood cultured. Guidelines recommend a collection of 8 – 10 ml per culture bottle for a total of 40 ml per patient. Previous studies have demonstrated that suboptimal volume can lead to increased contamination and reduced true positive rates. This may lead to patients receiving un-necessary treatment or delays to directed antimicrobial therapy.

Aims: This study aimed to establish a reliable method of measuring the volume of blood in culture bottles taken in the ED, and then to employ this method to identify an association (if any) between BC volume, contamination and true positive rates sufficient to inform the design of a future interventional study.

Methods: This is a single site, prospective observational study. A customised device was used to record blood volume for all BC bottles sent to pathology for processing. The Kruskal – Wallace H test was used to examine the association between volume, true positive results and contamination.

Results: Preliminary results (first five weeks, n=541 BC bottles) demonstrated significant underfilling of BC bottles, with a median volume of 6mls (IQR 4mls – 10mls) per bottle and 165 (30.5%) bottles containing blood volume 4mls or less. Ongoing data collection and subsequent analysis will determine the relationship between BC volume and culture results.

Conclusion: Enquiry into the quality of blood cultures sent to pathology for testing has identified significant deviation from current volume guidelines, with substantial underfilling. The relationship between this underfilling and culture outcomes is currently being explored. Any identified association between BC underfilling and suboptimal test performance should be communicated to BC collectors so practice may be improved.


Mercedes is an experienced emergency nurse, having worked in senior positions in two of Queensland’s busiest hospitals. She is a passionate advocate for the improvement of patient care and has recently taken up the role of Clinical Nurse – Research within the Emergency and Trauma Centre at RBWH to work on the Bugs in Bottles project, a multidisciplinary research project aimed at improving the quality and use of blood cultures in the emergency department.

Angela Hills is a registered nurse working on the front line of health care at the Royal Brisbane and Women’s Emergency and Trauma Center. Angela places great emphasis on efficient and evidence-based care and became interested in clinical research with the hopes of improving practices in the emergency setting. Her interests include the treatment and diagnosis of sepsis and has recently joined a team looking into the quality of blood cultures in the emergency department.