Procalcitonin

What is Procalcitonin?

Procalcitonin (PCT) is a peptide precursor of the hormone calcitonin, and it plays a significant role as a biomarker for bacterial infections, especially sepsis.

  • Normally produced in small amounts by the thyroid gland.
  • During systemic bacterial infections, many tissues in the body begin producing PCT in large quantities.
  • Its levels rise rapidly (within 2–6 hours) in response to bacterial toxins and systemic inflammation

Why Is It Important in Sepsis?

  • Helps distinguish bacterial infections from viral or non-infectious causes of inflammation.
  • Higher levels of PCT are strongly associated with severe bacterial infections and sepsis.
  • It is used to:
    Diagnose sepsis early
    Monitor progression or resolution of infection
    Guide antibiotic therapy (e.g., when to start or stop antibiotics)

Interpreting Procalcitonin Levels

  • Low (<0.1 ng/mL): Bacterial infection unlikely
  • Moderate (0.1–0.5 ng/mL): Possible localized infection
  • High (>0.5 ng/mL): Suggestive of systemic bacterial infection or sepsis
  • Very high (>2 ng/mL): Strongly indicates sepsis or septic shock

Limitations

  • PCT can also rise in:
    Major surgery
    Severe trauma
    Certain cancers
  • It should not be used alone—clinical context and other tests are essential for accurate diagnosis.