PCT (Procalcitonin)

Procalcitonin (PCT) is a precursor protein of calcitonin, normally produced in very small amounts by the thyroid. In response to bacterial infection, PCT production rises rapidly and substantially, making it a valuable blood marker for identifying systemic bacterial infection and guiding antibiotic decisions. This test is suited to patients presenting with fever, suspected sepsis, or respiratory tract infections where the clinician needs to differentiate bacterial from viral causes, and to monitor response to treatment.

The sample is analysed using a quantitative immunoassay, providing a numerical PCT level that reflects the likelihood and severity of bacterial infection.

Biomarkers

Inflammation
- Procalcitonin (PCT)

Why it matters
PCT rises within 3 to 6 hours of bacterial infection, peaks at around 12 to 24 hours, and falls quickly as infection resolves. This kinetic profile makes it far more specific for bacterial infection than traditional markers such as CRP or white cell count, which can be elevated in viral illness, trauma, or autoimmune conditions. A low PCT can support the safe withholding or early discontinuation of antibiotics, reducing unnecessary antimicrobial exposure and helping to curb resistance. In suspected sepsis, a raised PCT supports prompt escalation of care, while serial measurements help track treatment success. For patients and clinicians alike, PCT offers a clearer, faster signal to guide timely and appropriate management.