This is a study to evaluate the diagnostic performance of the investigation NuQ. (R) H3.1 nucleosome assay as a diagnostic marker of sepsis in a population of patients admitted to critical care with signs suspicious of infection and consistent with the sepsis 3 definition. These patients will be compared to a group of adult surgical patients free from infection that are undergoing their first cardiac surgery.

This is a single centre, prosepctive study to evaluate the diagnostic performance of the investigation NuQ. (R) H3.1 nucleosome assay as a diagnostic marker of sepsis in a population of patients admitted to critical care with signs suspicious of infection and consistent with the sepsis 3 definition. The H3.1 assay is a chemiluminescent sandwich immunoassay for the detection of nucleosomes circulating in human plasma. The test quantifies the level of circulating nucleosomes and in conjunction with other laboratory findings and clinical assessment aids in the early detection of sepsis with organ dysfunction.

Inclusion Criteria:

• Patients must be at least 18 years of age to be included in the study.
• Patients must have been admitted to critical care emergently with signs and symptoms consistent with a possible diagnosis of sepsis: defined as one of these types of infections: respiratory system, renal and genito-urinary system, gastrointestinal and intra-abdominal system, central nervous system, musculoskeletal, sepsis or fever of unknown origin
• A 'comparator' arm will be included of patients aged over 18yrs of age undergoing planned elective coronary artery bypass graft surgery with anticipated post-operative care in critical care unit

Exclusion Criteria:

• Any subject not meeting the criteria above.
• Patients who are re-admitted to intensive care unit within the same hospital admission
• The exclusion criteria are designed to remove confounding effects from concomitant conditions that may render the interpretation of the NuQ.® H3.1 assay impossible. These circumstances are few, but exclusions will include patients with limitations of care, including 'Do not attempt resuscitation' orders.
• Patients with severe anaemia (as defined by a Hb<50g/dL) will be excluded.
• Subjects with any other severe concurrent disease that, in the judgment of the Principal Investigator, would make the subject inappropriate for entry into this study.
• Patients in the 'comparator' arm who are undergoing cardiac surgery will be excluded if they have an active infection and specifically patients with a suspected or confirmed diagnosis of infective endocarditis.
• Any patient undergoing cardiac surgery with a condition that might influence their immune response will be excluded. These include but are not limited to uncontrolled HIV, AIDS, uncontrolled systemic lupus erythematosus, rheumatoid arthritis or mixed connective tissue disorder, previous cancer and previous treatment with chemotherapy or the recipient of a solid organ or bone marrow transplant.

The participants will be recruited into two cohorts. The first cohort are patients who require critical care admission emergently from either A&E or other hospital ward with a presumed diagnosis of sepsis. The second group consists of patients who have a planned elective cardiac surgery (Coronary Artery By-Pass Graft surgery) and require critical care admission post operatively as part of the planned surgery. These patients have been selected to describe how the level of NuQ.® H3.1 alters over time after the sterile insult of cardiac surgery.