Blood cultures
Mastering blood cultures: the key to better outcomes
Although blood culture is arguably one of the most common and important diagnostic tests in the proper management of infectious diseases, it is frequently overlooked or underestimated. Yet blood cultures provide essential information for patient management. Failing to optimise their use, in particular through appropriate collection, processing and analysis, represents a missed opportunity for clinicians and ultimately for patients, warns Dr. Yoann Personne.
Blood cultures should be collected when a patient is suspected of having an infection, in particular in the case of sepsis (i.e. a severe infection, or an infection associated with organ failure), ideally before antibiotic administration. In addition, to using aseptic techniques, you also need to take into account sample volume and number of sets. National guidelines and recommendations stipulate that at least two sets of blood cultures (= two aerobic and two anaerobic bottles) should be collected with a volume of 8-10mL per bottle in adults (adequate blood volume for paediatric BC are mainly weight-dependent). The bottles should then be incubated in a blood culture analyser as soon as possible, ideally within a maximum of four hours.1,2
But is that the reality in clinical practice?
Findings from recent surveys and audits are quite alarming. A 2018 NHS England and NHS Improvement survey1
demonstrated that 87%
of sites took only one set (rather than the recommended two) and only 3% of UK sites incubated blood cultures bottles within four hours of collection. In 40% of cases, time from sample collection to incubation was more than 24 hours! Regarding the volume of blood, which is a key parameter to ensure detection of bacteremia or fungemia, the vast majority of Trusts (88%) did not measure the collected volume of blood and 41% had, in fact, never audited their blood culture workflow altogether.
Why it is everyone’s problem Let’s take a step back to examine where the issue might lie. The journey of a patient’s sample begins from the moment it is collected. Rather than viewing samples as an isolated laboratory test, it is crucial to adopt an end-to-end pathway approach that takes into account the entire process. The NHS England survey highlighted the often-overlooked pre-analytic phase, where microbiology staff have little input. Therefore,
it would be unfair to solely fault the laboratory for the issues described. To ensure optimal patient benefits, a sensible approach requires consideration of three phases: pre-analytical, analytical, and post-analytical. As staff members will vary throughout this pathway, a multi- disciplinary approach should be integrated making it everyone’s responsibility. Every year 100,000 bloodstream infections (BSIs) are diagnosed in the UK.1
BSIs are a serious
medical condition that can lead to sepsis, multiple organ failure and death, if not managed promptly and adequately. Blood cultures are a key component of the ‘Sepsis Six’ and ‘Surviving Sepsis’ bundles. Despite recognition of their importance, little attention is given to optimise their potential to improve patient management. The medical need for blood cultures is clear: identify the pathogen causing the infection to provide and tailor the appropriate treatment. In some cases, the detection of positive results allows to correct an inadequate
empirical antimicrobial therapy, or stepping down from broad spectrum agents to a targeted therapy. In neonatal medicine, a negative 36- hour blood culture may allow early cessation of antimicrobials and discharge. Ultimately, this improves the use of antimicrobials. Additionally, a positive detection provides clues to identify the site of infection (especially in patients with fever of unknown origin or sepsis). Finally, it carries implications for both infection control and public health.
Is broad spectrum really a good answer? Sepsis guidelines stipulate early initiation of empiric antimicrobial therapy in order to reduce morbidity and mortality, as well as review and de-escalation when possible. Unfortunately, the overall turnaround time for BSI diagnosis is rather slow. Until the causing pathogen and its associated susceptibility profiles are known, patients receive empiric antimicrobial
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