Activation of blood platelets is a typical finding in patients with systemic inflammation and sepsis.They seem to mediate key pro-inflammatory mediator secretion, immune-cell activation while their adhesion to the endothelium enhances the pro-coagulatory activity of endothelial cells impairing microcirculation thus, may lead to multiple organ dysfunction. However, the exact effects of bacterial products on platelet function have not been found to be consistent and may vary according to the species, the timing of the study, and the pathogenesis of sepsis. Data vary, including both increased and decreased platelet reactivity and aggregation among patients with sepsis compared to healthy controls. Defining platelet's behaviour during sepsis is particularly important in view of recent findings revealing potential association between antiplatelet therapy and reduction in short term mortality, incidence of acute lung injury and intensive care unit admission in critically ill patients.This study aims to measure P2Y12 mediated platelet reactivity, -using the point-of-care P2Y12 VerifyNow assay, in platelet reactivity units (PRU)- along different stages of sepsis, including bacteremia/uncomplicated infection, sepsis, severe sepsis and septic shock. Subgroup follow up of patients going along different stages will also be performed. At the end of this study analysis of clinical and laboratory findings in correlation with platelet reactivity will be performed to assess platelet aggregation during sepsis.

Inclusion Criteria:

• Patients presenting 0-8 hours post admission with signs of one of the following i) uncomplicated infection/bacteremia ii) sepsis iii) severe sepsis iv) septic shock
• 30 healthy subjects
• Signed informed consent

Exclusion Criteria:

• Pregnancy
• Breastfeeding
• Inability to give informed consent
• PLTs<70.000/ul or PLTs>741.000 ul
• Ht<25% or Ht>52%
• History of P2Y12 or GPIIb/IIIainhibitors the last 15 days prior assortment
• Patients with inherited (vonWillebrand factor deficiency, Glanzmann thrombasthenia, Bernard-Sulier syndrome) or established acquired platelet disorders (HIT)
• Patients undergoing hemodialysis
• History of gastrointestinal bleeding, genitourinary bleeding or other site abnormal bleeding within the previous 3 months.
• Previous history of immunologic disease (neoplasm, autoimmune disorders, HIV)
• Subjects receiving daily treatment with immune-modulating regimens.

Within 0-8 hours of presentation in emergency department patients will be assessed and assigned upon their health status in four distinct groups of uncomplicated infection/bacteraemia , sepsis, severe sepsis/septic shock as this is defined by International Sepsis Definitions Conference. Thirty five healthy volunteers will serve as a control group.