What is procalcitonin (PCT)?

Procalcitonin is a precursor peptide of calcitonin that rises sharply in response to bacterial infection and sepsis. Unlike CRP, it increases within 2–4 hours of a bacterial trigger and falls rapidly when infection resolves, making it useful for both diagnosis and treatment monitoring.

What units does PCT use?

PCT is reported in ng/mL or the equivalent mcg/L (1 ng/mL = 1 mcg/L). Some labs report in ng/dL — divide by 100 to convert to ng/mL before entering.

Can PCT alone diagnose sepsis?

No. PCT is a supportive biomarker, not a standalone diagnostic. It must be interpreted alongside clinical signs (fever, hypotension, altered mental status), SIRS/qSOFA criteria, culture results, and imaging. This tool provides interpretive guidance, not a diagnosis.

Why is PCT elevated in non-infectious conditions?

Major surgery, severe trauma, burns, and some non-infectious inflammatory states can raise PCT moderately (usually below 2 ng/mL). Very high PCT (>10 ng/mL) without a clear non-infectious cause strongly suggests systemic bacterial infection or sepsis.

How is PCT used to stop antibiotics?

Many protocols recommend discontinuing or de-escalating antibiotics when PCT falls by 80% from the peak value, or drops below 0.5 ng/mL, provided clinical improvement is also evident. This reduces antibiotic overuse.

Procalcitonin Helper

Enter a PCT value to get its clinical interpretation against established sepsis and antibiotic guidance thresholds.

Enter PCT Value

PCT Level

ng/mL and mcg/L are numerically equal. Divide ng/dL by 100.

Serial Values (optional)

Enter a PCT value to see its clinical interpretation

Clinical Threshold Reference

PCT (ng/mL)	Tier	Interpretation
< 0.1	Tier 1	Bacterial infection unlikely; antibiotics not indicated
0.1 – 0.25	Tier 2	Low likelihood; antibiotics discouraged unless high clinical suspicion
0.25 – 0.5	Tier 3	Possible bacterial infection; antibiotics may be considered
0.5 – 2.0	Tier 4	Probable systemic bacterial infection; antibiotics recommended
2.0 – 10	Tier 5	High probability of sepsis; prompt antibiotics indicated
> 10	Tier 6	Severe sepsis / septic shock likely; urgent broad-spectrum antibiotics

Thresholds per IDSA/ESCMID guidance. Always interpret in clinical context.

Copied!

Summary

Interprets procalcitonin (PCT) blood test values against clinical thresholds to guide sepsis likelihood assessment and antibiotic therapy decisions. PCT rises rapidly in bacterial infections and sepsis while staying low in viral infections, making it a key biomarker for antibiotic stewardship.

How it works

Enter the PCT value from the blood test report.
Select the unit (ng/mL is standard; mcg/L is numerically equivalent).
The tool maps the value to the established 6-tier clinical threshold table.
A color-coded result shows the infection likelihood tier and antibiotic guidance.
Serial values can be entered to track treatment response over time.

Use cases

Assessing likelihood of bacterial vs. viral infection in febrile patients.
Supporting decisions on initiating or withholding antibiotic therapy.
Guiding antibiotic de-escalation when PCT falls during treatment.
Monitoring response to sepsis therapy with serial PCT measurements.
Teaching clinical reasoning about inflammatory biomarkers.

Frequently Asked Questions

Last updated: 2026-06-18 · Reviewed by Nham Vu