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PCT Overview

What is Procalcitonin (PCT)?

PCT is the prohormone of the hormone calcitonin, but PCT and calcitonin are distinct proteins. Calcitonin is exclusively produced by C-cells of the thyroid gland in response to hormonal stimuli, whereas PCT can be produced by several cell types and many organs in response to pro-inflammatory stimuli, in particular by bacterial products.

In healthy people, plasma PCT concentrations are found to be below 0.05 ng/ml, but PCT concentrations can increase up to 1000 ng/ml in patients with sepsis, severe sepsis or septic shock. PCT Values below 0.5 ng/ml almost rule out severe sepsis or septic shock. PCT levels above 2 ng/ml are highly suggestive of an infectious process with systemic consequences and represent a high risk for progression to severe sepsis or septic shock. PCT values in the range of 0.5 and 2 ng/ml represent a "grey" zone with uncertainty as far as the diagnosis of sepsis is concerned.

The induction of PCT can be caused by different stimuli both in vitro and in vivo. Bacterial endotoxins and pro-inflammatory cytokines are powerful stimuli for the production of PCT. The exact biological role of PCT remains largely unknown, however, recent experimental studies suggest that PCT may play a pathogenic role in sepsis. The PCT protein carries leukocyte chemoattractant properties and modulates the production of NO by endothelial cells.

PCT is a stable protein in plasma and blood samples. At room temperature, more than 80% of the initial concentrations can be recovered after 24 hours of storage, and > 90% is recovered when the sample is kept at 4 °C. Plasma PCT has a normal half life of 25 - 30 hours, and 30 - 45 hours in patients with severe renal dysfunction.

A significant elevation of plasma PCT is found during sepsis, but particularly during the early days of severe sepsis and septic shock. Early on, after multiple trauma or major surgery, in severe burns or in neonates, PCT levels can be elevated independently of an infectious process. The return to baseline is usually rapid and in these cases a second increase of PCT can be interpreted as the development of a sepsis episode. Viral infections, bacterial colonization, localized infections, allergic disorders, autoimmune diseases, and transplant rejection do not usually induce a significant PCT response (values < 0.5 ng/ml).