Prokalsitonii

Procalcitonin (PCT), sometimes transliterated as prokalsitonin in non-English texts, is a peptide precursor of calcitonin. In healthy individuals serum procalcitonin levels are typically less than 0.05 ng/mL. During systemic bacterial infections, levels rise markedly; viral infections generally cause little or no rise, though there are exceptions.

Physiology: Procalcitonin is produced by neuroendocrine cells and, during infection, by many other cell types in response to pro-inflammatory stimuli such as endotoxins and cytokines (IL-6, TNF-α, IL-1β). The rise occurs within hours and correlates with severity in sepsis.

Clinical use: Procalcitonin testing is used to support differential diagnosis between bacterial and non-bacterial causes of inflammation and to guide antibiotic therapy. In lower respiratory tract infections, PCT levels help decide whether antibiotics are needed and when to discontinue. Typical thresholds (various assays) approximate: <0.1 ng/mL unlikely bacterial infection; 0.1–0.25 ng/mL possible; 0.25–0.5 ng/mL borderline; ≥0.5 ng/mL suggests bacterial infection; ≥2 ng/mL raises concern for sepsis. Clinicians combine PCT with clinical assessment and other tests.

Limitations: PCT can be elevated in major surgery, trauma, burns, pancreatitis, renal failure, and some fungal infections; it may be low in localized infections or early in disease; different immunoassays yield different values; therefore thresholds are assay- and context-dependent.

Measurement and interpretation: PCT is measured by immunoassays on serum, plasma, or whole blood; turnaround is typically a few hours. Use is guideline-driven and should not replace clinical judgment.