What are the causes of elevated Procalcitonin (PCT) levels?

Causes of Elevated Procalcitonin (PCT) Levels

Bacterial infections, particularly sepsis and severe sepsis, are the primary causes of significantly elevated procalcitonin levels, with septic shock typically causing levels >10 ng/mL. 1

Primary Causes of Elevated PCT

Infectious Causes

• Bacterial infections:
  • Sepsis (2-10 ng/mL) 1
  • Severe sepsis (>2 ng/mL) 1
  • Septic shock (>10 ng/mL) 1
  • Bacterial pneumonia 1
  • Ventilator-associated pneumonia 1
  • Bacterial co-infections in viral illnesses 1

Non-Infectious Causes

• Major trauma 2:
  • Multiple injuries with abdominal trauma (3-4 ng/mL)
  • Liver/gut trauma (4-5 ng/mL)
  • Combined liver/spleen and thorax trauma (>9 ng/mL)
• Burns (severe) 3
• Acute myocardial infarction (median 3.57 ng/mL at 24h) 4
• Major surgery 5
• Cardiogenic shock 4
• Post-resuscitation 4
• Post-cardiac surgery 4
• Electrical burns (can cause very high levels, mean 15.7 ng/mL) 3

PCT Level Interpretation

PCT Level	Clinical Interpretation
<0.1 ng/mL	Likely viral infection or non-infectious condition [6]
0.1-0.25 ng/mL	Low probability of bacterial infection [6]
0.25-0.5 ng/mL	Possible bacterial infection [6]
0.5-2.0 ng/mL	Systemic inflammatory response syndrome (SIRS) [1]
>2.0 ng/mL	High likelihood of sepsis [1,6]
>10 ng/mL	Severe sepsis or septic shock [1,6]

Important Clinical Considerations

• PCT rises rapidly within 2-3 hours of bacterial infection onset 1
• Peak levels typically occur at 6-24 hours 1, 6
• PCT has a half-life of 22-35 hours 1
• Serial measurements are more valuable than single measurements 1, 6
• PCT levels are not elevated in chronic inflammatory states 1
• PCT has higher specificity for bacterial infections than CRP (77% vs 61%) 6

Factors Affecting PCT Interpretation

• False positives:

  • Severe trauma, especially with abdominal involvement 2
  • First 24-48 hours post-major surgery 1
  • Acute myocardial infarction 4
  • Severe burns 3

• Interfering factors:

  • Renal function (affects clearance) 1
  • Different techniques of renal replacement therapy 1
  • Neutropenia 1
  • Severe viral illnesses like COVID-19 or influenza 6

Clinical Applications

• PCT >0.5 ng/mL suggests the need for antibiotic therapy 6
• PCT-guided antibiotic stewardship can reduce antibiotic use 1, 6
• PCT levels ≥5 ng/mL are associated with increased mortality in trauma patients 7
• In COVID-19, PCT can help identify bacterial co-infections or secondary infections 1
• A 50% rise in PCT compared to previous values suggests secondary bacterial infection in critically ill patients 1

Remember that while PCT is a valuable biomarker, it should always be interpreted in the clinical context and alongside other diagnostic findings rather than in isolation.