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.

K.N., T.D.Y., D.S., J.T.K., S.C., R.F.D. and R.B.B. declare they are present or past employees or shareholders of Immunexpress, Inc. W.M. declares that she is a present employee of Princeton Pharmatech, Inc. R.R.M. III discloses that, over the time period of relevance to this work he was paid (as a consultant) an honorarium by Immunexpress for conducting a critical review of a Clinical Evaluation Report of SeptiCyte technology, submitted by Immunexpress to the Therapeutic Goods Administration (TGA) of Australia. N.R.A. declares that he has received grants from the NIH and Department of Defense for non-related work, and that payments from these grants are made to his institution, the University of Colorado. No other competing interests are declared.

This work was funded by Immunexpress, Inc.

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Ethics approval for the MARS trial was given by the medical ethics committee of AMC, Amsterdam (approval # 10-056C, 16 June 2010). Ethics approvals for the VENUS trial were given by the relevant Institutional Review Boards as follows: Intermountain Medical Center/Latter Day Saints Hospital (approval # 1024931, 21 January 2014); Johns Hopkins Hospital (approval # IRB00087839, 28 January 2016); Rush University Medical Center (approval # 15111104-IRB01, 11 March 2016); Loyola University Medical Center (approval # 208291, 10 March 2016); Northwell Healthcare (approval #16-02-42-03, 1 April 2016). Ethics approvals for the NEPTUNE trial were given by the relevant Institutional Review Boards as follows: Emory University (approval # IRB00115400, 3 December 2019); Grady Memorial Hospital (approval # 00-115400, 14 January 2020); Rush University Medical Center (approval # 19101603-IRB01, 16 January 2020); University of Southern California Medical Center (approval # HS-19-0884-CR001, 10 February 2020). All methods used in this study were carried out in accordance with the relevant guidelines and regulations. Informed Consent Statement: All subjects, or their legally authorized representatives, gave informed consent for participation in this study.

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