Procalcitonin (PCT) helps to differentiate bacterial from viral infections. The early detection of elevated PCT levels in patients with suspected bacterial infections enables earlier antibiotic treatment. PCT also supports informed decisions on when to continue or stop antibiotics, improving patient care and decreasing antibiotic misuse and resistance.
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 proinflammatory stimuli, in particular by bacterial products.
In healthy people, plasma PCT concentrations are found to be below 0.05 μg/L, but PCT concentrations can increase up to 1 000 μg/L in patients with sepsis, severe sepsis or septic shock. Usually, PCT concentrations exceeding 0.5 μg/L are interpreted as abnormal values suggestive of a sepsis syndrome. PCT values in the range of 0.5 and 2 μg/L represent a “grey” zone with un certainty as far as the diagnosis of sepsis is concerned. In these cases, it is recommended to repeat the measurement after 6 – 24 hours, until a specific diagnosis is identified. PCT levels above 2 μg/L are highly suggestive of an infectious process with systemic consequences. Concentrations above 10 μg/L are almost ex clusively found in patients with severe sepsis or septic shock. Find out more about the PCT reference values for patients with sepsis or lower respiratory track infection.
One major advantage of PCT compared to other parameters is its early and highly specific increase in response to bacterial infections and sepsis.
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 ex perimental studies suggest that PCT may play a pathogenic role in sepsis. The PCT protein carries leukocyte chemoattractant pro perties 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. In patients with non-bacterial “SIRS”, PCT levels are usually found to be in the lower range (<1 μg/L). However, early 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 colonisation, localised infections, allergic disorders, autoimmune diseases, and transplant rejection do not usually induce a signi f i cant PCT response (values <0.5 μg/L).