Sepsis is a complex condition with time⍰dependent evolution, and longitudinal biomarker dynamics may improve its characterisation. We hypothesised that biomarker kinetics are associated with sepsis, the intensity of organ dysfunction, and patient survival. This single⍰centre, prospective, observational study included adult patients presenting to the Emergency Department with suspected infection and a National Early Warning Score 2 (NEWS2) ≥3. Blood samples were collected at baseline, 4 and 24 hours. Linear mixed models assessed associations between biomarker trajectories, sepsis diagnosis, and organ dysfunction severity. Joint models evaluated the predictive value of biomarker kinetics during the first 24 hours for in⍰hospital mortality. Of 214 screened patients, 173 were analysed and 137(79%) developed sepsis. Linear mixed models showed significant time⍰dependent decreases in IL10(β −0.016, 95%CI −0.028 to −0.004), IL1RN(β −0.014, 95%CI −0.024 to −0.004), and IL6(β −0.012, 95%CI −0.024 to 0.00). Sepsis diagnosis was associated with higher IL1RN(β 0.378, 95%CI 0.153– 0.603) and TNFRSF1A(β 0.40, 95%CI 0.21–0.58); a significant interaction between sepsis and time was observed only for IL6. Increasing SOFA scores correlated with elevated IL10(β 0.048), IL1RN(β 0.044), CCL2(β 0.046), TNFRSF1A(β 0.050), and procalcitonin(PCT; β 2.63), all p<0.01. The SOFA–time interaction was significant only for IL6 (β −0.003, 95%CI −0.005 to −0.001). Joint survival models adjusted for age and maximum SOFA identified IL8 (HR 0.655, 95%CrI 0.582– 0.728), TNFRSF1A (HR 0.505, 95%CrI 0.419–0.682), and PCT (HR 1.004, 95%CrI 1.001– 1.008) as outcome predictors. In conclusion, sepsis and organ dysfunction severity are associated with distinct inflammatory biomarker levels and kinetics. IL6 showed a unique time⍰dependent relationship, while TNFRSF1A, IL8 and PCT dynamics were associated with survival.

Background/Objectives: Routine biomarkers and clinical scores do not directly assess functional immune responsiveness in suspected sepsis. We evaluated whether the TNF-α Release Assay (TARA), a whole-blood LPS-induced functional assay, is associated with an early cytokine-low immune phenotype in Emergency Department (ED) patients. Methods: In this prospective single-center cohort, adults with suspected sepsis and NEWS2 ≥ 3 were sampled at presentation, at 4 h and, when available, at 24 h. Immune phenotypes were defined independently of TARA by unsupervised k-means clustering of 12 circulating cytokines at 4 h, and a continuous Low-Response Cytokine Score (LRCS) was derived, with higher values indicating lower global cytokine concentrations. Results: Among 152 patients, three phenotypes were identified: C1 cytokine-low (n = 56), C2 inflammatory/intermediate (n = 63), and C3 IFN-γ/MCP-3/IL-17A-high (n = 33). Indicative TARA low-response status was independently associated with a higher LRCS after adjustment for clinical covariates and procalcitonin (PCT), both at presentation (β = 0.33; 95% CI, 0.14–0.53; p = 0.001) and at 4 h (β = 0.38; 95% CI, 0.19–0.57; p < 0.001). Indicative TARA low-response results at 4 h were most frequent in C1 and least frequent in C3 (75% vs. 45%). Exploratory clinical comparisons showed lower recorded early escalation in C1, whereas Sepsis-3 final diagnosis and in-hospital mortality were similar across phenotypes. Conclusions: A TARA low-response status was independently associated with an early circulating cytokine-low phenotype defined without reference to TARA or outcomes, providing information complementary to routine biomarkers and clinical severity scores. These exploratory findings support TARA as a complementary functional immune readout but require external validation and clinical-impact evaluation.