In-depth analysis of sampling practice and yield of blood cultures

PURPOSE: To describe BC collection practices at a tertiary care university hospital in a prospective observational study and examine the association between blood volume and culture yield. METHODS: Analysis of all blood cultures collected during a 6-week period in 2023 at St Olav's University Hospital, Norway. Additionally, we analysed impact of antimicrobial treatment prior to sampling, sampling department, bottle type, sampling time and method, microorganisms isolated as well as patient age and sex. RESULTS: Only 19.7% of BC bottles were filled with the recommended 8-10 mL of blood. The overall pathogen positivity rate of all BC bottles was 6.8%, while 13.3% of the patients had at least one positive BC bottle. Patients >60 years were twice as likely to have a positive blood culture as those aged 18-60 years (16.2% vs 8.1%). Recommended filling volumes were positively associated with recovery of microbes, whereas particularly overfilling >14 mL was associated with reduced microbial yield. Overall, bottles with no growth contained a significantly higher mean blood volume than bottles with growth. CONCLUSION: This study highlights the gap between established recommendations for BC collection and current practice at our hospital. Preanalytical optimisation of BC collection is needed to improve diagnostic yield in this seriously ill patient population. Overfilling of BC bottles was negatively associated with microbial yield and should be avoided.