Diagnostic and Prognostic Value of Serial PCT Measurements in Critically Ill Patients

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.