Procalcitonin

Procalcitonin (PCT) is a peptide precursor of the hormone calcitonin, secreted in regulated fashion to reduce serum calcium concentration in order to maintain calcium homeostasis. Under  normal physiological  conditions, PCT is produced  mainly by  thyroidal  c-cells  and  in  small amounts  in  neuroendocrine  cells  of  lung  and  small intestine  respectively.  Here it is further processed into its effective hormone calcitonin and stored in cellular vesicles until released in conditions of high serum Ca level. Calcitonin decrease the calcium absorption by inhibiting activity of osteoclasts, which are responsible for breaking down bone; thus proper serum levels of calcium is maintatined in the circulation. Hence, PCT is nearly not detectable in serum of normo-calcaemic patients.

 

The level of PCT increases in response to any shock like state, trauma, surgery and pro-inflammatory stimuli especially of bacterial origin making it as an acute phase reactant. Generally, viral infections are characterized by IFN-γ activation, attenuate the PCT production. On the other hand, the high PCT levels produced during bacterial infections are not followed by a parallel increase in calcitonin or serum calcium levels. Because of these characteristics of PCT, it has been used as a specific serum biomarker in differentiating bacterial and nonbacterial etiology.

 

PCT levels are raised much earlier during an infectious process in comparison with CRP (4–12 hours vs 24–38 hours), which facilitates earlier diagnosis. PCT can be used as a prognostic marker as its levels correlate with bacterial load and severity of infection, which is not the case for CRP. Q-line® Platinum PCT is a latex enhanced immuno-turbidimetric assay. PCT in the sample bind to the specific anti-PCT antibody coated on to latex particles and cause agglutination. The degree of the turbidity caused by agglutination is optically measured.