Procalcitonin (PCT)

A more specific marker for bacterial infection than CRP.

What it is

Procalcitonin is a precursor protein to calcitonin. Under normal conditions levels are very low, but they rise steeply and specifically during bacterial infections — far more so than during viral infections or non-infectious inflammation.

Why it matters

In immunocompromised patients (including those on chemotherapy), distinguishing bacterial infection from treatment-related inflammation is critical. PCT helps guide that decision. A rising PCT during treatment is an early warning to escalate to your medical team.

How to test

Blood test. Usually ordered in a clinical context — ask your oncologist to include it if you have fever during treatment.

This information is for educational purposes only. Always discuss testing and interpretation of results with your care team.

Optimal range

Below 0.1 ng/mL

normal

0.1–0.5 ng/mL

low bacterial infection risk

Above 0.5 ng/mL

possible bacterial infection or sepsis risk

How often

During febrile episodes or suspected infection. Not a routine monitoring marker.