What Is Procalcitonin?
Procalcitonin (PCT) is a precursor to the hormone calcitonin. Normally it is produced in tiny amounts, but bacterial infections — especially serious ones — trigger a massive spike in PCT within 4–6 hours. Viral infections typically do not raise PCT significantly.
Procalcitonin Interpretation
| PCT Level | Interpretation |
|---|---|
| < 0.1 ng/mL | Normal — bacterial infection very unlikely |
| 0.1–0.25 ng/mL | Low risk — viral infection likely; antibiotics usually not indicated |
| 0.25–0.5 ng/mL | Borderline — clinical judgment required |
| 0.5–2.0 ng/mL | Moderate risk — bacterial infection probable; antibiotics likely indicated |
| > 2.0 ng/mL | High risk — severe bacterial sepsis likely |
| > 10 ng/mL | Septic shock — very high mortality risk |
Why Is It Useful?
- Helps doctors decide whether antibiotics are needed
- Reduces unnecessary antibiotic prescribing (antibiotic stewardship)
- Serial PCT levels monitor response to treatment — levels should fall with effective antibiotics
- Used in ICU and emergency settings for sepsis diagnosis
Limitations
- Can be raised by non-infectious causes (major surgery, severe trauma, some cancers)
- Can be normal in localised bacterial infections (abscess, early pneumonia)
- Fungal infections do not typically raise PCT
PCT vs CRP in Infection
CRP rises more slowly (peaks at 48 hours) and is less specific — it rises with any inflammation including viral. PCT rises faster and more specifically with bacterial infection, making it the preferred acute marker.
FAQs
Is procalcitonin ordered routinely?
No — it is used specifically in acute illness settings, sepsis workup, and respiratory infections where antibiotic decisions are being made.
Can I test procalcitonin privately?
Yes — some private labs offer it, but it's primarily a hospital test.
How quickly do levels fall with treatment?
PCT should fall by 50% or more every 24–48 hours with effective antibiotics.
Medical Disclaimer: Procalcitonin is one of many tools in diagnosing infection — clinical judgement always takes precedence over a single result.