Interpreting biomarkers in infectious diseases in intensive care unit: the potential role of procalcitonin

Life threatening organ dysfunction in the critically is always due to or accompanied with some kind of dysregulated immune response. This is not the privilege of sepsis only, as the host response is not specific for the type of the insult. Therefore, similar reactions are provoked by both infectious or non-infectious injuries. This similarity in the host response makes differential diagnosis difficult and often leads to false interpretation of biomarkers that have been used in diagnosing sepsis and infection for several decades. Today we understand that damage and pathogen associated molecular patterns, the PAMPs and DAMPs, are more-or-less identical regardless of the type of the insult. One of the most studied biomarkers in this field is procalcitonin (PCT). It is true, that absolute values show a huge scatter amongst patients admitted with similar diseases and conditions due to the individual response of patients for a given insult, therefore difficult to interpret, but this holds true for any biomarker. However, due to its half-life of 24 hours, evaluating the kinetics of PCT based on a series of regular measurements makes it a potentially very useful marker on the intensive care unit. It can help the clinician’s decision making in several ways. It may be used for the diagnosis of infection; assessing antibiotic appropriateness; diagnosing cytokine storm and evaluating the patient’s inflammatory response in general, both in infections and after non-infectious injuries. PCT may also help to provide additional information to indicate adjunctive immunomodulation therapies, such as immunoglobulins or extracorporeal cytokine removal, etc., in several shock states. The aim of this review is to put PCT in a different context as reported previously and provide the pathophysiological rationale of why and how one should use it at the patients’ bedside.