In 2005, the Food and Drug Administration (FDA) approved procalcitonin in conjunction with other laboratory markers to aid in the risk assessment of critically ill patients with severe infection (sepsis). Although considerable literature exists regarding the usefulness of Procalcitonin (PCT) as a marker of sepsis, there are still potential uses for PCT measurements that are not yet explored and its value among the critically ill patients remains unclear. This study seeks to better understand the usefulness of measuring PCT values in patients admitted to the Medical ICU for a variety of reasons and in particular with severe infection (sepsis).

Procalcitonin (PCT) is a 116 amino acid peptide that has an approximate MW of 14.5 kDa and belongs to the calcitonin (CT) superfamily of peptides. Transcription of the CALC-1 gene for PCT is usually suppressed in the non-neuroendocrine tissue, except in the C cells of the thyroid gland where its expression produces PCT, the precursor of CT in healthy individuals and in the absence of infection.

In the presence of microbial infection, circulating levels of calcitonin precursors (CTpr), including PCT, increase up to several thousand-fold.1 In addition to being a marker of microbial infection, PCT also acts as a modulator of the host inflammatory reaction. In an animal model of sepsis, administration of exogenous human PCT worsened outcome, whereas neutralization of endogenous PCT improved survival.

There are several inflammatory laboratory markers, like tumor necrosis factor (TNF)-α, interleukin (IL)-1, IL-6 and C-reactive protein (CRP), but they are non- specific for infection and can be caused by conditions like pancreatitis, burns, trauma or acute lung injury. The non-specific nature of clinical and laboratory parameters for microbial infection makes it difficult to evaluate patients with potential infection. In addition to the lack of specificity, traditional laboratory and clinical indicators of sepsis are not temporally concordant with the course of illness. As a result, these tests are not reliable to evaluate the response to therapeutic interventions in real time.

Inclusion Criteria:

• All consecutive patients admitted to the Medical Intensive Care Unit of the Cleveland Clinic with an anticipated MICU stay of ≥ 12hrs

Exclusion Criteria:

• Age less than 18-years of age and/or an expected MICU stay of less than 12-hrs

Prospective-observational study design in which a PCT measurement will be obtained on admission to the Medical Intensive Care Unit (MICU) and then daily (as clinically available)until discharge from the unit or death.