PCT Molecule & Kinetics

Molecule & Stability

Procalcitonin (PCT) is a 116 amino acid protein with a sequence identical to that of the prohormone of calcitonin (32 amino acids). Under normal metabolic conditions, hormonally active calcitonin is produced and secreted in the C-cells of the thyroid gland after specific intracellular proteolytic procession of the prohormone PCT. In severe bacterial infections and sepsis, however, intact PCT is found in blood.

In vivo PCT molecule is very stable with an in vivo half-life time of 22-29 hours. Since the PCT is also very stable in vitro, there are no special requirements to pre-analytical sample handling and storage.

Figure 2

PCT Kinetics

PCT increases after 2-3 hours after induction e.g. by endotoxin and may increase to levels up to several hundred nanogram per ml in severe sepsis and septic shock. After successful treatment intervention the value decreases, indicating a positive prognosis. Persistently high or even further increasing levels are indicators for poor prognosis.

After induction, e.g. by endotoxin, PCT increase is observed within 2-3 hours. Levels then rise rapidly, reaching a plateau after 6-12 hours. PCT concentrations remain high for up to 48 hours, falling to their baseline values within the following 2 days. The half-life is about 20 to 24 hours.

(Meisner M., Procalcitonin (PCT) A new, innovative infection parameter. Biochemical and clinical aspects, ISBN: 3-13-105503-0, Thieme Stuttgart, New York 2000).

Figure 3

The graph shows PCT plasma concentrations (ng/ml) in a 76 year old female patient, following an infusion solution accidentally contaminated with Acinetobacter baumanii. The induction period can be described according to 2 types of kinetics: during the first phase (<6h), PCT increased by approximately 0.5 ng/ml per hour after a latency phase of about 2-3 hours (first measurable value recorded at time = 3h) followed by massive PCT production at the rate of approximately 50 ng/ml per hour over subsequent hours (Brunkhorst F.M. et al., Intens Care Med 1998, 24: 888-892).