PCT is not elevated in autoimmune, allergic, and viral infections. Localized limited bacterial infections, minor infections, and chronic inflammation do not cause its elevation. Bacterial endotoxin plays a crucial role in the induction process.
PCT reflects the activity of systemic inflammatory response. Factors that affect PCT levels include the size and type of infected organ, the type of bacteria, the degree of inflammation, and the state of the immune response. In addition, PCT is only detectable 1 to 4 days after major surgery in a small number of patients.
Elevated PCT levels are seen in severe shock, systemic inflammatory response syndrome (SIRS), and multiple organ dysfunction syndrome (MODS), even in the absence of bacterial infection or bacterial lesions. However, PCT levels in these cases are usually lower than those in patients with bacterial lesions. The release of cytokines from the gut or bacterial translocation may cause induction.