The investigators seek to evaluate a new test for determining presence of infection/sepsis as compared to non-infection/systemic inflammatory response syndrome among critically ill patients within the first 24 hours of their being hospitalized in an intensive care unit (ICU) within the first 7 days of hospitalization. The primary purpose of the study is to validate SeptiCyte® Lab in this population as compared to: 1) the doctor's impression and 2) existing clinical parameters. The investigators also hope to assess how well a related, new blood test, SeptID® identifies different types of infection, as compared to cultures and other lab tests.

Inclusion Criteria:

1. 18-89 years old on the day of ICU admission

2. SIRS present as defined by the presence of two or more of the following:

   • Temperature > 38°C or < 36°C
   • Heart Rate > 90 beat/min
   • Tachypnea > 20/min or PaCO2 < 32 mmHg
   • White Blood Cell count > 12 000/mm3 or < 4 000/mm3 or > 10% immature neutrophils (bands)

Exclusion Criteria:

1. Consent not provided
2. Age less than 18 or greater than 89 years old on the day of ICU admission
3. Not admitted to ICU
4. Clinical cultures or serologies not obtained
5. Subject has been admitted to study hospital (or transferring facility) for ≥ 24 hours
6. Elective cardiac surgery patients with an expected duration in ICU of less than 24 hours.
7. Patients on non-prophylactic antibiotics for more than 24 hours prior to ICU admission
8. Delay of >24 hours between trial enrollment and sample draw time
9. Ethnic/racial category has completed enrollment.

Critically ill subjects, admitted to an Intensive Care Unit