PCT was first described by Bohoun in 1992 as the precursor molecule of human calcitonin (molecular weight of 13 kD). The polypeptide of 116 amino acids comprises an N-terminal region, the midregional calcitonin and the C-terminal region of katacalcin.
In healthy persons, PCT is quickly processed by proteolysis into calcitonin and its other regional fragments. The normal plasma concentrations are under the detection limit of the PCT assay of 0.01 ng/ml. In contrast, very high levels of PCT are typical in patients with systemic bacterial infections, sepsis or multiorgan failure. In these cases, PCT concentrations of over 100 ng/ml have been measured without any changes in plasma calcitonin . The hormonally active region of calcitonin has a very short half-life of 10-20 mins. In contrast, PCT has an ideal halflife of about 24 hours and lacks hormonal activity .
In comparison with interleukins, PCT is a very stable protein in vivo and in vitro. At room temperature, PCT values remain constant and measurable for several hours. Stored frozen, the activity remains unchanged for 6 months. Repeated thawing and freezing has been found to have no influence on the PCT molecule .
PCT is analysed using the immunoluminometric assay LUMItest® PCT (BRAHMS Diagnostica, Berlin, Germany). This test system determines PCT quantitatively in human serum or plasma. It is easy to handle and can be performed in less than 3-4 hours. Inter- and intra-assay variations at both low and high concentrations are less than 7%.
The biological function of PCT and the major organs/tissues of origin are still uncertain. PCT cannot be induced in vitro, by allogeneic, lectin or endotoxin stimulation of peripheral blood or isolated cell populations . Equally as unknown as the cellular origin of PCT is the function of PCT.
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