Silvia Cermelli

Background: Accurate early identification of sepsis remains a major clinical challenge due to its heterogeneous presentation and overlap of clinical signs with the non-infectious systemic inflammatory response syndrome (SIRS). Timely differentiation is crucial for improving patient outcomes, meeting sepsis bundle requirements and reducing inappropriate antimicrobial use. We hypothesized that clinical–laboratory data available within the first three hours of patient presentation could be used to identify patients with sepsis at a clinically useful level of diagnostic accuracy, in lieu of traditional microbiology results which would not become available until at least 12–24 h. Data from two independent studies were used to quantify the diagnostic value of demographic, vital, clinical–laboratory, and microbiological data available at three time points for distinguishing retrospectively diagnosed critically ill patients with either sepsis or non-infectious SIRS. A particular focus of this work was an assessment of the utility of SeptiCyte RAPID (Immunexpress Inc., Seattle, WA, USA) as an aid to sepsis diagnosis, producing actionable data within one hour. Methods: Data from two independent study cohorts were analyzed. The “510(k) cohort” consisted of 419 adult patients in intensive care (ICU) (MARS, VENUS, and NEPTUNE studies). The “Andalusian cohort” consisted of 353 ICU patients from the PANGEA study. Logistic regression models, selected by a greedy search algorithm and validated by repeated cross-validation, were used to determine the contributions of different variables to diagnostic accuracy. Diagnostic performance was quantified by the area under the receiver operating characteristic curve (AUC). Results: For the 510(k) cohort, a baseline AUC of 0.69–0.73 was observed using five to seven vital and demographic variables assessed immediately upon presentation (time T1). The addition of clinical–laboratory variables, in particular SeptiCyte RAPID, within one to three hours post-presentation (time T2) increased the AUC to 0.85–0.86. Finally, the addition of microbiological data 12–24 h post-presentation (time T3) further improved the AUC to 0.90–0.91. Similar results were obtained for the Andalusian cohort. AUC values at the three time points were as follows: At time T1, AUC = 0.67 based solely on vital signs and demographics; at time T2, AUC = 0.87 based on vitals + demographics + SeptiCyte RAPID ± other clinical–laboratory data; at time T3, AUC = 0.93 based on vitals + demographics + SeptiCyte RAPID ± other clinical–laboratory data + microbiology results. For both cohorts, the most significant variables included temperature, mean arterial pressure, respiratory rate, suspected infection site, SeptiCyte RAPID, procalcitonin, confirmed bacterial infection and positive blood culture confirmation. In summary, the AUC for diagnosing sepsis rose progressively from T1 (510(k) 0.69–0.73; Andalusian 0.67) to T2 (510(k) 0.85–0.86; Andalusian 0.87) with the addition of SeptiCyte RAPID to T3 (510(k) 0.90–0.91; Andalusian 0.93) as more clinical information became available over time. Conclusions: The accuracy of identification of sepsis increases markedly as demographics and vital signs are supplemented with clinical–laboratory information, and ultimately with microbiological culture results. The AUC improves in the shortest time within the first three hours when laboratory data, and particularly SeptiCyte RAPID results, become available. Integrating rapid host response testing with SeptiCyte RAPID into time-based diagnostic frameworks may enhance early sepsis recognition, improve antimicrobial stewardship, and support guideline-driven clinical decisions.

OBJECTIVES: Biomarkers with adequate precision to rule-in/rule-out sepsis in children represent an unmet need. SeptiCyte RAPID is a point-of-care, U.S. Food and Drug Administration-cleared, host gene expression biomarker test for the determination of sepsis probability (reported in 1 hr as a SeptiScore) using a small-volume peripheral blood sample. We have previously reported on SeptiCyte RAPID performance in adults. Here we report a retrospective, noninterventional clinical validation study of SeptiCyte RAPID, as a sepsis diagnostic adjunct in children. DESIGN, SETTING, AND PATIENTS: Critically ill children ( n = 284), 1 month to 18 years old, admitted to PICUs, with or without suspected or documented infection, but all of whom met criteria for systemic inflammatory response syndrome (SIRS) and were enrolled at multiple clinical sites in the United States and Australia in four separate studies. INTERVENTIONS: None; SeptiCyte RAPID results were not used to guide patient treatment. MEASUREMENTS AND MAIN RESULTS: A combination of clinical adjudication and an independent panel of three physicians (Retrospective Physician Diagnosis [RPD]), blinded to SeptiCyte RAPID results, were used to retrospectively categorize patients into sepsis vs. noninfectious SIRS categories. Diagnostic performance of SeptiCyte RAPID for differentiating sepsis and noninfectious SIRS compared with RPD was measured using area under the curve (AUC), likelihood ratio, and a monotonic increase in probability of sepsis and increasing SeptiScores. Binomial logistic regression analysis was used to integrate clinical parameters in a model based on SeptiCyte RAPID. Higher SeptiScores correlated with higher probability of sepsis. SeptiCyte RAPID AUC for identifying sepsis in children ranged from 0.80 to 0.83. A model additionally integrating lactate, platelet number, mean arterial pressure, Pa co ₂ , mechanical ventilation, weight, age, and leukocyte count increased SeptiCyte RAPID performance (AUC, 0.86; 95% CI, 0.85–0.87). CONCLUSIONS: SeptiCyte RAPID demonstrated similar performance characteristics in children to that previously reported for adults. Additional real world effectiveness studies are warranted to determine real-time clinical utility, patient benefits, and health economic impact.

Overview: SeptiCyte RAPID is an FDA-cleared gene expression test that quantifies host immune response to aid in the diagnosis of sepsis. The test yields a score (the SeptiScore) ranging from 0–15, distributed across four bands (1–4) based on increased likelihood of sepsis. Each band can be characterized by average positive and negative likelihood ratios (LR+ and LR−, respectively) for the discrimination of sepsis versus the non-infectious systemic inflammatory response syndrome (SIRS). Methods: A retrospective analysis of prospectively collected data from a combined cohort of critically ill patients suspected of sepsis (n = 889), recruited across 19 hospitals in the USA and Europe. The analysis quantified the LR+ and LR− parameters as a function of SeptiScore, for discrimination of sepsis vs. SIRS in patients admitted to ICU. Hypotheses: (1) The likelihood ratio (LR) framework provides a clinically useful interpretive approach that complements the previously used SeptiScore banding scheme; (2) Low Band 1 SeptiScores are associated with sufficiently small LR− to support the use of SeptiCyte RAPID as a rule-out test for sepsis; (3) High Band 4 SeptiScores are associated with sufficiently large LR+ to support the use of SeptiCyte RAPID as a rule-in test for sepsis; and (4) SeptiScore-derived LR+ and LR− values can be combined with estimates of pre-test probability (derived from patient characteristics and/or other diagnostic tests) to generate individualized, patient-specific post-test probabilities of sepsis. Results: The SeptiCyte RAPID test demonstrates strong diagnostic performance in distinguishing sepsis from SIRS. The likelihood ratios across different score bands provide clear clinical utility: the median LR+ was 3.26 (range 2.57–4.24) for Band 3, and 6.97 (range 4.35–15.57) for Band 4, providing evidence toward ruling in sepsis at high SeptiScores. Conversely, the median LR− was 0.16 (range 0.14–0.20) for Band 2 and 0.085 (range 0.014–0.16) for Band 1, providing evidence toward ruling out sepsis at low SeptiScores. A higher-resolution analysis of SeptiCyte RAPID performance confirmed these trends by evaluating LR+ and LR− at specific values within each band. The sepsis group was further stratified according to whether patients were classified as blood culture positive (BC+) or blood culture negative (BC−), and the detailed LR+ and LR− analyses were repeated. A monotonic increase in likelihood ratio with increasing SeptiScore was consistently observed, independent of whether sepsis patients were culture-positive, culture-negative, or unstratified with respect to blood culture status. Conclusions: High SeptiScores have correspondingly high LR+ values, and low SeptiScores have correspondingly low LR− values, both of which may have clinical utility. High likelihood ratios for Band 4 SeptiScores, which precede traditional microbiology results, may provide clinicians with early confidence of a sepsis diagnosis and microbiology diagnostic stewardship. Low likelihood ratios for Band 1 SeptiScores may prompt clinicians to consider an alternate diagnosis to sepsis. These are diagnostic-performance-based observations; whether they translate into fewer missed diagnoses or more efficient use of hospital resources has not been directly assessed in this study and will require dedicated clinical outcome studies.

Background: Early diagnosis and identification of causative pathogens using blood culture in patients suspected of blood stream infection (BSI) and sepsis are critical for improving patient outcomes through earlier and more targeted treatment. There is a need for tools that can guide the use of microbiologic diagnostics, especially where resources are limited, such as in lower- and middle-income countries (LMICs), pandemic and mass-casualty scenarios, and prolonged field care settings during military operations. Methods: Post hoc retrospective analysis of individual patient data from three prospective clinical studies, conducted in North America, Europe and Africa, to investigate the association between SeptiCyte RAPID test results (SeptiScores) and blood culture (BC) results. Hypothesis: that a significant correlation exists between elevated SeptiScores and positive blood culture results, and between low SeptiScores and negative blood culture results. Results: The area under the receiver operating characteristic curve (ROC AUC) was 0.91 for 85 BC(+) versus 257 SIRS and was 0.80 for 164 BC(−) versus 257 SIRS. As the SeptiScore increases, the relative probability of a septic patient being BC(+) as opposed to BC(−) also increases. A non-linear positive correlation is observed. Below a crossover point at SeptiScore 10, the ratio of probabilities of BC(+) sepsis/BC(−) sepsis is 1. Thus, septic patients with SeptiScores >10 have a higher probability of being BC(+) compared to BC(−). Conclusions: Elevated SeptiScores, obtained before blood culture results, are indicative of increased blood culture positivity. This may have clinical utility, particularly in resource-limited settings, as an aid for improving the efficiency of blood culture practice, for instance, by informing patient selection and interpretation of blood culture results.

Background/Objective: SeptiCyte RAPID is a transcriptional host response assay that discriminates between sepsis and non-infectious systemic inflammation (SIRS) with a one-hour turnaround time. The overall performance of this test in a cohort of 419 patients has recently been described [Balk et al., J Clin Med 2024, 13, 1194]. In this study, we present the results from a detailed stratification analysis in which SeptiCyte RAPID performance was evaluated in the same cohort across patient groups and subgroups encompassing different demographics, comorbidities and disease, sources and types of pathogens, interventional treatments, and clinically defined phenotypes. The aims were to identify variables that might affect the ability of SeptiCyte RAPID to discriminate between sepsis and SIRS and to determine if any patient subgroups appeared to present a diagnostic challenge for the test. Methods: (1) Subgroup analysis, with subgroups defined by individual demographic or clinical variables, using conventional statistical comparison tests. (2) Principal component analysis and k-means clustering analysis to investigate phenotypic subgroups defined by unique combinations of demographic and clinical variables. Results: No significant differences in SeptiCyte RAPID performance were observed between most groups and subgroups. One notable exception involved an enhanced SeptiCyte RAPID performance for a phenotypic subgroup defined by a combination of clinical variables suggesting a septic shock response. Conclusions: We conclude that for this patient cohort, SeptiCyte RAPID performance was largely unaffected by key variables associated with heterogeneity in patients suspected of sepsis.

Background SeptiCyte RAPID is a transcriptional host response assay that discriminates between sepsis and non-infectious systemic inflammation (SIRS) with a one-hour turnaround time. The overall performance of this test in a cohort of 419 patients has recently been described [Balk et al., J Clin Med 2024, 13, 1194]. In this study we present results from a detailed stratification analysis in which SeptiCyte RAPID performance was evaluated in the same cohort across patient groups and subgroups encompassing different demographics, comorbidities and disease, sources and types of pathogens, interventional treatments, and clinically defined phenotypes. The aims were to identify variables that might affect the ability of SeptiCyte RAPID to discriminate between sepsis and SIRS, and to determine if any patient subgroups appeared to present a diagnostic challenge for the test. Methods 1) Subgroup analysis, with subgroups defined by individual demographic or clinical variables, using conventional statistical comparison tests. 2) Principal component analysis and k-means clustering analysis, to investigate phenotypic subgroups defined by unique combinations of demographic and clinical variables. Results No significant differences in SeptiCyte RAPID performance were observed between most groups and subgroups. One notable exception involved an enhanced SeptiCyte RAPID performance for a phenotypic subgroup defined by a combination of clinical variables suggesting a septic shock response. Conclusions We conclude that for this patient cohort SeptiCyte RAPID performance was largely unaffected by key variables associated with heterogeneity in patients suspected of sepsis.

(1) Background: SeptiCyte RAPID is a molecular test for discriminating sepsis from non-infectious systemic inflammation, and for estimating sepsis probabilities. The objective of this study was the clinical validation of SeptiCyte RAPID, based on testing retrospectively banked and prospectively collected patient samples. (2) Methods: The cartridge-based SeptiCyte RAPID test accepts a PAXgene blood RNA sample and provides sample-to-answer processing in ~1 h. The test output (SeptiScore, range 0–15) falls into four interpretation bands, with higher scores indicating higher probabilities of sepsis. Retrospective (N = 356) and prospective (N = 63) samples were tested from adult patients in ICU who either had the systemic inflammatory response syndrome (SIRS), or were suspected of having/diagnosed with sepsis. Patients were clinically evaluated by a panel of three expert physicians blinded to the SeptiCyte test results. Results were interpreted under either the Sepsis-2 or Sepsis-3 framework. (3) Results: Under the Sepsis-2 framework, SeptiCyte RAPID performance for the combined retrospective and prospective cohorts had Areas Under the ROC Curve (AUCs) ranging from 0.82 to 0.85, a negative predictive value of 0.91 (sensitivity 0.94) for SeptiScore Band 1 (score range 0.1–5.0; lowest risk of sepsis), and a positive predictive value of 0.81 (specificity 0.90) for SeptiScore Band 4 (score range 7.4–15; highest risk of sepsis). Performance estimates for the prospective cohort ranged from AUC 0.86–0.95. For physician-adjudicated sepsis cases that were blood culture (+) or blood, urine culture (+)(+), 43/48 (90%) of SeptiCyte scores fell in Bands 3 or 4. In multivariable analysis with up to 14 additional clinical variables, SeptiScore was the most important variable for sepsis diagnosis. A comparable performance was obtained for the majority of patients reanalyzed under the Sepsis-3 definition, although a subgroup of 16 patients was identified that was called septic under Sepsis-2 but not under Sepsis-3. (4) Conclusions: This study validates SeptiCyte RAPID for estimating sepsis probability, under both the Sepsis-2 and Sepsis-3 frameworks, for hospitalized patients on their first day of ICU admission.