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INTRODUCTION Sepsis is a life-threatening organ dysfunction caused by dysregulated host response to infection. Early detection of sepsis is very crucial in its management, as there is an increase of 8% mortality for every hour delay in commencing therapy (Kumar et al., 2006). A wide variety of diagnostic techniques proposed, could not be clinically translated due to poor sensitivity & specificity, high levels of heterogeneity and complexity of assay preparation. Currently most clinical settings depend on Procalcitonin (PCT) and C-reactive protein (CRP) for diagnosis, which also lack sensitivity and specificity. The objective of our study was early detection of sepsis in patients undergoing cardiac surgery. Blood stream infection, confirmed by blood culture (the gold standard), requires large turnaround time and is less sensitive here due to prophylactic antibiotics. SOFA score overestimate the probability of sepsis due to the impaired cardiovascular parameters and inotrope support (Howitt et al., 2018). The Society of Thoracic Surgeons (STS) criteria to detect sepsis need positive blood culture to identify sepsis within the first 48 hours post-surgery. Since none of the above can cater early diagnosis, the most appropriate way is to target dysregulated host response. It has been reported that increased expression of CD64, on neutrophil surface (nCD64) is associated with proinflammatory response and down-regulation of HLA-DR expression on circulating monocytes (mHLA-DR) is associated with anti-inflammatory response in humans. Citing this interplay between pro and anti-inflammatory response in sepsis, we hypothesized that the relative expression of these antigens may detect dysregulated host immune response and thereby may provide a criterion for early diagnosis of sepsis MATERIALS AND METHODS A flowchart of the experimental steps is shown in Fig1. Adult patients, who underwent cardiac surgery, were selected for this double-blinded study after the approval from the appropriate Institutional Ethics Committee. The study was un-blinded after the initial set of experiments, with biochemical and clinical outcome of the patients. The data sets were analyzed (GraphPad Prism v8.1.1) and a p value of < 0.05 was considered statistically significant RESULTS Out of the total patients (n=33), 7 patients were diagnosed with suspected sepsis and 1 with proven sepsis as per STS criteria, substantiated by longer ICU and hospital stay (Table1). The optimized Flowcytometry panel and gating strategies is shown in Fig.2 The expression of nCD64, mHLA-DR and SI (Sepsis Index) in all patients before surgery did not show any statistically significant difference with that of healthy controls [Figure-3A]. At 24 hours post-surgery, all patients had significant up-regulation of nCD64 and down-regulation of mHLA-DR. A similar significant elevation was observed in CRP and PCT [Figure-3 B-D], but insignificant difference exists between sepsis and non-sepsis patients (p values in Table1). Therefore the diagnostic efficacy of all this measurements and scoring scheme, in identifying sepsis at 24 hours was poor (Table2) A useful diagnostic criterion is obtained by calculating the fold increase in nCD64 (I64) & SI (ISI) and fold decrease in mHLA-DR (DHLA) at 24 hour. It was observed that many patients had ISI≥10, due to I64 approximately 2 and DHLA 5. Based on this observation, a diagnostic criterion able to detect 'dysregulated host immune response' at 24 hour post-surgery is identified. The criterion is: 10 fold or more increase in SI combined with either ≤1.8 fold increase in nCD64 or ≤5.2 fold decrease in mHLA-DR. CONCLUSION The data obtained from this pilot study was analysed based on different criteria to identify the best possible way to detect the onset of sepsis post-cardiac surgery. The discriminative power of many tests to differentiate sepsis and SIRS is inadequate. We propose a combination of fold changes in antigen expression, which could so far, identify all sepsis patients, since the measurements detect the underlying biological mechanism, picking up both exacerbated proinflammatory response and immunoparalysis. The significance of the result is that the proposed diagnostic criteria could potentially pre-empt diagnosis of sepsis at 24 hours post-surgery, before the onset of any clinically identifiable symptoms of the disease. This needs to be substantiated by extending the study on a larger patient cohort. Disclosures Mony: BD Biosciences: Research Funding. Jain:BD Biosciences: Employment.

INTRODUCTION Sepsis caused by a dysregulated host response to infection, is a serious healthcare problem that results in very high mortality every year-round the globe. When left untreated, sepsis can potentially turn fulminant, making early diagnosis and intervention an essential component of the therapeutic strategy. Proinflammatory cytokines are necessary for initiating an effective inflammatory response against infection, whereas their excess production has been associated with tissue injury in multiple organ systems leading to increased mortality. In contrast, anti-inflammatory cytokines seem to be a prerequisite for controlling and down regulating the initial inflammatory response. But a sustained release of these biomolecules leads to a turn-down of immune activation within the host organism. In the clinical conundrums associated with sepsis, it was often observed that pathogen-responsive cells were exposed to a complex cytokine milieu. The excess production of proinflammatory cytokines is essential for the survival, replication and activation of phagocytic and cytotoxic immune cells. In conjunction with this proinflammatory activity, anti-inflammatory cytokines are also released which are involved in the occurrence of cellular anergy and impaired response to aetiologic agents, causing a compensatory anti-inflammatory response syndrome (CARS). Current practice in cardiac surgery is to review laboratory test results (CRP, PCT, blood culture) and clinical criteria (SOFA and STS) 48 h after surgery to diagnose sepsis. CRP and PCT lack sensitivity and specificity, whereas blood culture requires a long turnaround time and lacks sensitivity. Sepsis being an interplay between pro and anti-inflammatory response, the relative expression of immune biomarkers may provide a useful criterion for early diagnosis of sepsis. Thus, we aimed at investigating the variations in circulating levels of prominent cytokines and their potential use as a diagnostic marker of adult sepsis post cardiac surgery. MATERIALS AND METHODS In this double-blinded cohort study, blood samples of adult patients undergoing cardiac surgery were collected before surgery (D -1), and on the post-operative day 1 (D +1) after the approval from the appropriate Institutional Ethics Committee. Patients who were deemed risky by EuroSCORE II risk stratification were included and immuno-compromised as well as patients with active infection before surgery were excluded. Plasma levels of IL-1β, IL-5, IL-6, IL-10, IL-17A and TNFα were determined using cytometric bead assay by flow cytometry and the results were analyzed using FCAP Array™ software. The data sets were analyzed (GraphPad Prism 5.02) and a p value of &lt; 0.05 was considered statistically significant. RESULTS The study was conducted with 34 patients (n=34) and un-blinded after retrieval of data. The cohort has 8 patients diagnosed with sepsis and 26 without sepsis based on STS criteria. Demographic details for both groups are summarized in Table 1. Cytokine and other biomarker expression levels before (D-1) and after (D+1) Surgery is summarized in Table 2. At D +1, IL-1β, TNF-α, IL-17A and IL-10 showed significantly higher concentration in sepsis group compared to non-sepsis group (Fig 1B). CRP, PCT, WBC and differential blood count were not showing any discriminatory potential between sepsis and non-sepsis patients at D +1. The ROC curves of the above four cytokine expression levels at D+1 was analyzed between sepsis and non-sepsis groups. A plasma IL-1β level of 0.25 pg/ml had a sensitivity of 87.5 % and a specificity of 53.8 % and a plasma IL-17A level of 1.78 pg/ml had a sensitivity of 75 % and specificity of 46.2 %. In addition, IL-10 level of 8.99 pg/ml in plasma showed a diagnostic sensitivity of 87.5 % and a specificity of 53.8% (Fig 1C). Based on the current observation we proposed a model of inflammatory cytokine dynamics involving IL-1β, IL-17A and IL-10 suggesting their role, which may lead to the development of sepsis (Fig 1D). CONCLUSION We identified a significant up regulation of circulating inflammatory cytokines at 24 h in patients who developed sepsis after cardiac surgery, earlier than any noticeable changes in conventional sepsis biomarkers. These results suggest the possibility of inflammatory cytokines as a diagnostic marker and may be a potential therapeutic target as well. The study needs to be validated further on a larger cohort of patients. Figure 1 Figure 1. Disclosures No relevant conflicts of interest to declare.