Increasing the volume of blood received in adult paired blood culture bottles at a regional public health laboratory: results of a quality improvement project to optimise the diagnosis of bacteraemia.

Background: Optimising the diagnosis of bacteraemia has clinical, infection control and antimicrobial stewardship benefits. It's well documented that volume of blood received in blood culture bottles affects test sensitivity. The ability of blood cultures to detect bacteraemia is proportional to the volume of blood cultured. We undertook a period of baseline measurement and established that mean blood culture fill volume was inadequate.

Aim: The primary aim was to increase the percentage of adequately filled blood cultures (≥5ml) by 20% and increase the percentage of optimally filled bottles (8-10ml) by 10% in six months (by 1st August 2018). Our secondary aim was to increase the mean volume in blood culture bottles to 8ml (by 1 August 2018). We measured the clinical impact of this on test sensitivity by comparing blood culture positivity rate between adequately and inadequately filled bottles.

Methods: Following a period of baseline measurement we implemented three phases of plan/do/study/act (PDSA) intervention cycles (including a small test pilot cycle). Interventions were focused around user education/engagement, real time user feedback and laboratory reporting. User questionnaires were administered to investigate knowledge and practice; further informing the interventions.

Results & Conclusion: Between 1 March - 1 August 2018 the mean volume of blood inoculated into culture bottles rose from 5ml (95% CI 4.1-6.0ml) to 7.5ml (95% CI 6.4-8.5ml). The percentage of adequately-filled (≥5ml) blood culture bottles increased from 47% to 61% (absolute increase of 14%) and the percentage of optimally-filled (≥8ml) bottles increased from 16% to 29% (absolute increase of 13%). Although our project didn't fully meet its aims, we observed a significant and sustained improvement in filling of blood culture bottles.