Procalcitonin (PCT)
Procalcitonin is a precursor of the hormone calcitonin, normally present in blood at very low levels. It rises sharply in response to bacterial infection and systemic inflammation (sepsis) but remains largely unchanged in viral infections or non-infectious inflammation. PCT is used in hospitals to distinguish bacterial from viral infections and to guide decisions about starting or stopping antibiotics.
Reference Ranges
Male
0 – 0.05
ng/mL
Female
0 – 0.05
ng/mL
Child
Consult pediatrician
Reference ranges may vary by laboratory. Always compare with the range printed on your lab report.
What Low Levels Mean
PCT below 0.05 ng/mL is normal and makes significant bacterial infection unlikely. In patients with suspected infection, a low PCT supports withholding or stopping antibiotics, particularly in lower respiratory tract infections where viral cause is common.
What High Levels Mean
PCT above 0.5 ng/mL suggests bacterial infection. Above 2 ng/mL strongly suggests sepsis, and above 10 ng/mL indicates severe sepsis or septic shock. PCT can also rise after major surgery, burns, or trauma without infection — clinical context matters.
Frequently Asked Questions
Why is procalcitonin useful when we already have CRP?
CRP rises with any inflammation — infection, autoimmune disease, trauma, or cancer. PCT is far more specific for bacterial infection and rises and falls faster. PCT-guided antibiotic protocols have been shown to safely shorten antibiotic courses and reduce unnecessary antibiotic use.
Can procalcitonin be used for diagnosing COVID-19?
No. Viral infections including COVID-19 usually produce only mild PCT elevation. A rising PCT in a COVID patient suggests secondary bacterial pneumonia, which changes treatment. PCT cannot diagnose or rule in COVID itself.
Can PCT be falsely high without infection?
Yes. Major trauma, major surgery, severe burns, cardiogenic shock, medullary thyroid cancer, and the first 24–48 hours of life in newborns can raise PCT without bacterial infection. Trends over time are more informative than any single value.
Related Inflammation tests
See all →C-Reactive Protein (CRP)
Blood marker that rises with inflammation or infection.
mg/LInflammationESR (Erythrocyte Sedimentation Rate)
Non-specific marker of inflammation — how fast red cells settle.
mm/hrInflammationHigh-Sensitivity CRP (hs-CRP)
Precise CRP measurement used for cardiovascular risk assessment.
mg/LThis information is for educational purposes only and should not replace professional medical advice. Always consult your doctor for interpretation of your test results.
Read Full Medical Disclaimer →