A clinical study presented at the Sepsis Update Congress 2025 demonstrates the potential of rapid diagnostics to transform the management of patients with suspected sepsis. The culture-free blood test detected nearly three times more bloodstream infections than conventional blood cultures, with markedly faster results. Could these findings pave the way to a new approach to sepsis care?
Here, lead researcher Antoine Dewitte, Pathologist at Bordeaux University Hospital, explains the findings and their implications for patient outcomes.
What diagnostic gap does the culture-free sepsis test address?
In intensive care unit (ICU) patients with suspected sepsis, clinicians need microbiological confirmation quickly to guide therapy, yet conventional blood cultures are slow and often negative, particularly after antibiotics have started.
Detecting bacteria in blood is intrinsically challenging because bloodstream pathogen loads can be extremely low – sometimes only a few organisms in a standard blood-culture volume. This diagnostic uncertainty promotes initiation and continuation of broad-spectrum antibiotics and can delay timely de-escalation.
Our clinical aim was therefore threefold: to obtain organism identification earlier than blood cultures when bacteremia is present; to provide an earlier, reliable rule-out of bacteremia when results are negative, enabling prompt diagnostic reassessment; and to increase overall microbiological yield under real-world ICU conditions, while benchmarking performance against concomitantly collected blood cultures as the reference comparator.
Can you walk us through how the assay works?
The assay adopts a culture-independent, direct-from-blood workflow designed to enrich intact bacterial cells before genomic identification. In practice, the assay is built to “clear the noise” first, then read the bacterial signal.
Whole blood undergoes a differential lysis step that removes human cells and reduces background DNA, including free circulating DNA. Intact bacterial cells are then selectively lysed, and their DNA is extracted and amplified using a pan-pathogen PCR, before real-time sequencing with nanopore sequencing technology.
The intended advantage is to deliver clinically meaningful microbial identification within hours, without waiting for bacterial growth.
From a diagnostic perspective, what does the assay's integrated approach enable that single-modality tests cannot?
The culture-free assay preferentially targets bacteria with an intact cell envelope (presumed viable), rather than free circulating microbial DNA. This is important because whole blood is an extremely challenging matrix for genomics: human DNA is overwhelming. After antibiotics or tissue injury, microbial DNA fragments may persist and do not necessarily reflect live pathogens.
By reducing free DNA and enriching intact bacterial cells prior to sequencing, the assay aims to improve the signal-to-noise ratio and reduce ambiguity compared with approaches that read free DNA alone, including direct-from-blood NGS strategies (broad metagenomic sequencing, mNGS, or targeted sequencing such as 16S).
In addition, it is not restricted to a predefined organism panel, unlike many multiplex PCR assays. Conceptually, it helps bridge the gap between classical culture (viable organisms, but slow and antibiotic-sensitive) and nucleic-acid tests (fast, but sometimes difficult to interpret in low-biomass samples), with the goal of delivering earlier, clinically actionable microbiological information.
What were the key findings of the study regarding assay sensitivity?
The assay showed very high sensitivity versus concomitantly collected blood cultures in our prospective ICU cohort of 107 patients. In the paired analysis, sensitivity of the culture-free assay was close to 95 percent and the negative predictive value close to 98 percent. In terms of positivity, 45 of 372 (12 percent) blood-culture bottles were positive, whereas 123 of 246 (50 percent) culture-free tests were positive, reflecting a substantially higher detection yield.
Importantly, some of these additional culture-free assay detections were supported by pathogens recovered from clinically relevant site-of-infection samples and/or subsequent blood cultures.
What factors do you think account for the difference in sensitivity compared with gold standard analysis?
A central issue is that blood cultures – while a necessary comparator and reference standard – are an imperfect “gold standard” in ICU practice. First, bloodstream infection can be low-level and intermittent, so any single blood draw can miss the event simply because very few bacteria are present at that moment. Beyond that, culture requires viable bacteria to grow under laboratory conditions, whereas the culture-free assay is designed to detect intact bacterial cells directly from blood without relying on growth.
In addition, prior or ongoing antibiotics can suppress growth, and some organisms are slow-growing, fastidious, or anaerobic. Together, these factors can plausibly contribute to discordant results and the higher positivity observed with the culture-free assay.
The test demonstrated a median turnaround time of just over five hours. How significant is time to result when managing patients with suspected sepsis in the ICU?
In ICU sepsis care, hours matter. A 5-hour median turnaround time represents a major reduction compared with conventional blood-culture workflows. Using the gold standard method, organism identification took on average 37 hours in our study, and negative cultures are typically only finalized after five days.
In clinical practice, most ICU patients with suspected sepsis receive antibiotics very quickly, which is essential but also contributes to prolonged broad-spectrum exposure under uncertainty. Earlier microbiological information can therefore be reassuring for clinicians: a rapid positive result may support the suspected diagnosis and help align therapy with the likely pathogen, while a rapid negative result – given the assay’s very high negative predictive value – may support earlier diagnostic reassessment and stewardship decisions rather than waiting days for cultures to finalize as negative.
The assay frequently identified organisms that were missed by blood cultures but found in site-specific samples. How should clinicians interpret these findings when correlating results with clinical context?
In ICU patients – especially with abdominal or pulmonary sources – fastidious or mucosa-associated organisms can be clinically relevant, but they should be interpreted with caution. We recommend reading these results within a clinical–microbiological framework that integrates the suspected focus, site-of-infection microbiology, and blood-culture results.
In our study, all positive episodes with the culture-free assay were adjudicated using a prespecified framework, and roughly two-thirds had concordant microbiological support. In practice, detections corroborated by site-of-infection cultures are the most actionable and can be taken into account when tailoring antimicrobial therapy. Importantly, the frequent concordance between culture-free detections and pathogens recovered from the presumed site of infection raises the possibility that bacterial passage into the bloodstream may occur more often than we typically capture with blood cultures.
How does the assay perform on samples from patients already receiving antibiotics, and why is that particularly important in real-world ICU practice?
Antibiotic exposure is the rule rather than the exception in ICU. In our cohort, 91 percent of patients were already receiving systemic antibiotics at the time of sampling, including 78 percent on broad-spectrum therapy, meaning the assay was evaluated under real-world, antibiotic-exposed conditions. This is particularly important because intensivists often cannot afford to delay or under-treat suspected sepsis, yet antibiotic exposure is precisely what can reduce blood-culture yield and prolong diagnostic uncertainty. Because the culture-free assay is designed to detect intact bacterial cells directly from blood without relying on growth in culture, it is well aligned with this common ICU scenario.
What additional validation or implementation steps are needed before culture-free assays could be integrated into routine clinical workflows?
The next steps will include multi-center validation and impact studies embedding culture-free testing into ICU decision-making pathways. These will confirm performance and determine whether earlier microbiological information translates into measurable benefits for patients and antibiotic use.
Evaluating the assay in more targeted populations, such as endocarditis and pediatrics, could further refine and strengthen its clinical value. Rapid identification directly from blood could become a powerful lever for antibiotic stewardship, helping to reduce unnecessary exposure to broad-spectrum agents and, consequently, selection pressure for resistance.
In addition, despite the lack of phenotypic susceptibility testing, future studies could explore whether serial testing and rapid signal clearance under antibiotics might provide supportive information on microbiological response. At the same time, broader adoption will require regulatory clearance and, ultimately, reimbursement supported by robust evidence of clinical utility and health-economic value.
How might culture-free testing reshape the diagnostic paradigm for sepsis?
More broadly, our findings also raise a scientific question: the frequent detection in blood of organisms that matched pathogens recovered from the presumed site of infection suggests that bloodstream exposure may occur more often than we typically capture with blood cultures. If confirmed, this could open a new research avenue in sepsis and host–pathogen interactions—examining how transient or low-intensity bloodstream events relate to immune responses, clinical deterioration, and outcomes. Ultimately, this points toward a more dynamic sepsis diagnostic paradigm that combines rapid pathogen detection with host-response profiling.
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