MICROBIOLOGY


Collection to load time and blood volumes do not have a demonstrable impact on laboratory workflows if the processes for these are suboptimal. In fact, if not done appropriately, the reduction in pathogen isolation will reduce the laboratory work-up needed, however, while often overlooked these steps in the pathway can also impact patient management and contribute to mortality.10,11


With the executive summary report and the new SMI, a focus on time to instrument and blood fill volumes will now put a spotlight on pre-analytical activities, the success or failure of which may need to be monitored by the laboratory.


n 88% of trusts never measured blood culture volume.7 These findings were just some of the examples of the guidelines not being followed. B37 already recommended two sets of blood cultures for the majority of patients and that 20-30mL of blood be cultured per set. In fact, the executive summary indicated that, just by adhering to the existing standards, a number of improvements could be made to the pathway overall, including reducing the time to identification of causative organism, improved antimicrobial stewardship and infection control procedures, targeting of therapy and ultimately improving patient outcomes. On this basis and through review and analysis of the survey, NHS England made four recommendations: n Build upon existing national guidance and best practice


n Implement local monitoring to identify areas for improvement with a focus on two main quality indicators; blood fill volume and time to load


n Antimicrobial stewardship (AMS) and Antimicrobial resistance (AMR) to be a core part of clinical leadership and trust governance


n Improve regulation and accreditation.7 So, while it may have appeared at first glance that the executive summary


was calling for a renaissance of blood culture pathway practices, it only calls for a closer adherence to the guidance already in place. The only additional ask is a move to closer monitoring and audit of the information pertaining to the pre analytical aspects of the blood culture pathway, namely ‘collection-to-load time into the incubator’ and ‘volume of blood’.2


Why focus on these two areas in particular? One would think that a focus on contamination may be required, but the reality is that most laboratories and hospital teams in general are aware of contamination and may already be focusing on education and quality initiatives around this, as contamination has a tangible impact on the laboratory and clinical follow up. The additional resources put into the processing of bottles that flag positive with ‘likely contaminants’ is measurable.8


Anyone


who’s worked in a 24/7 laboratory has known the feeling of processing a sample in the small hours of the morning just to have all the effort written off as contamination. And what about the patient? Evidence suggests that these false positives result in unnecessary treatment and prolonged hospital stays – bad for the patient and an additional cost burden to the healthcare system.9


While it may have appeared at first glance that the executive summary was calling for a renaissance of blood culture pathway practices, it only calls for a closer adherence to the guidance already in place


44


Collection to load time Time to instrument is a critical step in the blood culture pathway. Essentially the collection to load time will determine how soon (or not) the bottles are placed into an appropriate incubator and can actually begin the ‘culture’ phase. Best practice for the transport and loading in blood cultures remains as soon as possible, with four hours as the maximum time allowed for transport before an impact on results. Delaying the incubation of the bottle can reduce the number of live organisms within the sample, increasing the time it takes for the sample to flag positive and can allow the overgrowth of contaminant organisms masking the true cause of infection.12


Any delay beyond the recommended four hours will, in essence, elongate the blood culture pathway by that amount of time as a minimum. While you may be correct in thinking that ‘hardy’ organisms such as E. coli or S. aureus which represent around 30%13


of blood stream


infections (BSI) will grow regardless, it has been suggested that the shortened time to flag on the instrument will not compensate for the initial delay or for the increased risk of false negatives.14 Further to this, there is evidence that this delay can also impact the result itself, increasing the time taken for bottle to flag positive or prevent the isolation of the organism at all.15


This delay can have


a domino effect, delaying or preventing the identification and subsequent antimicrobial sensitivity testing of the organism and thus preventing targeted therapy for the patient. Conversely, adapting work practices to facilitate bottle loading outside of the typical ‘office hours’ or indeed outside of the lab has shown demonstrable positive impacts on patient management and antimicrobial stewardship.16,17


Blood culture volumes Blood culture fill volume is again, critical when it comes to maximising the accuracy of the information we get from a blood culture result with sensitivity raising from 73.1% for one set, to 89.7% for two sets and 98.3% for three sets.18


This means nothing if these JUNE 2023 WWW.PATHOLOGYINPRACTICE.COM


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