Normal Values for Procalcitonin (PCT)
Normal procalcitonin levels are typically <0.1 ng/mL in healthy individuals, with values between 0.1-0.25 ng/mL suggesting a low risk of bacterial infection and values >0.25 ng/mL indicating an increased likelihood of bacterial infection. 1, 2
Reference Ranges for Procalcitonin
- Normal/healthy individuals: <0.1 ng/mL 3
- Low risk of bacterial infection: 0.1-0.25 ng/mL 1
- Possible bacterial infection: 0.25-0.5 ng/mL 4
- Likely bacterial infection: >0.5 ng/mL 2
- Severe bacterial infection: 2-10 ng/mL 2
- Septic shock: >10 ng/mL 2
Clinical Interpretation of PCT Values
Lower Values
- PCT levels <0.1 ng/mL have a high negative predictive value for bacterial infection 2
- Values between 0.1-0.25 ng/mL suggest a low probability of bacterial infection but cannot completely rule it out 4
- Some patients with bacterial community-acquired pneumonia may still have low PCT levels, with reported sensitivity for bacterial infection ranging from 38-91% 4
Elevated Values
- PCT levels >0.25 ng/mL indicate an increased likelihood of bacterial infection 4
- Values >2 ng/mL have been associated with severe sepsis with a sensitivity of 93.94% and specificity of 87.23% 5
- In bacterial meningitis, PCT values >10.2 ng/mL have shown high sensitivity and specificity (up to 100%) 2
Special Populations
- In end-stage renal disease patients, a higher cutoff value of 0.75 ng/mL (rather than 0.5 ng/mL) has been suggested for diagnosing infection, with a sensitivity of 76.2% and specificity of 80.0% 6
- In pediatric populations, PCT values >1 μg/L (equivalent to >1 ng/mL) have demonstrated better specificity (93%) and sensitivity (83%) than CRP for distinguishing between viral and bacterial infections 7
Clinical Applications and Limitations
- PCT should not be used alone to guide antibiotic therapy decisions, particularly in community-acquired pneumonia 4
- Higher PCT values strongly correlate with increased probability of bacterial infection, but no specific threshold can definitively discriminate between viral and bacterial pathogens 4
- PCT can be elevated in non-infectious conditions including shock states (cardiogenic, hemorrhagic) and certain drug reactions 2
- Serial PCT measurements may be more valuable than a single reading, particularly for monitoring treatment response 1
- PCT typically rises within 2-3 hours of infection onset, making it a useful early marker 2
Comparative Performance with Other Biomarkers
- PCT has demonstrated better specificity for bacterial infection compared to C-reactive protein in some studies 7
- However, in critically ill patients, PCT may not be a better marker of infection than CRP (sensitivity 67.6% vs 71.8%, specificity 61.3% vs 66.6%) 8
- The combination of PCT and CRP can increase the specificity for infection to 82.3% 8
Remember that while PCT is a valuable biomarker, clinical judgment remains essential when interpreting results, as no single threshold can definitively rule in or rule out bacterial infection in all clinical scenarios 4, 1.