What is the role of procalcitonin (PCT) in guiding antibiotic therapy in patients with suspected bacterial infections?

The Role of Procalcitonin in Guiding Antibiotic Therapy for Suspected Bacterial Infections

Procalcitonin (PCT) should be used to guide antibiotic discontinuation but not initiation in patients with suspected bacterial infections, particularly for respiratory tract infections and in critically ill patients. 1

Clinical Applications of Procalcitonin

Respiratory Tract Infections

• PCT has demonstrated significant value in guiding antibiotic therapy decisions for patients with suspected lower respiratory tract infections (LRTIs):
  • For patients with suspected LRTI who are likely to be admitted to the hospital, PCT-guided therapy is recommended (weak recommendation, moderate evidence) 1
  • For patients with acute exacerbation of asthma likely to be admitted, PCT guidance is suggested (weak recommendation, low evidence) 1
  • For patients with acute exacerbation of COPD likely to be admitted, PCT guidance is suggested (weak recommendation, moderate evidence) 1
  • PCT should NOT be used for patients with dyspnea and suspected/known heart disease 1

Sepsis and Critical Care Settings

• In sepsis patients, PCT can support:
  • Discontinuation of empiric antibiotics in patients who initially appeared to have sepsis but subsequently have limited clinical evidence of infection (weak recommendation) 1
  • Shortening the duration of antimicrobial therapy (weak recommendation) 1
  • PCT levels <0.5 μg/L or levels that decrease by ≥80% from peak can guide antibiotic discontinuation once patients stabilize 1

COVID-19 Patients

• Current evidence does not support routine use of PCT for antibiotic initiation decisions in COVID-19 patients
• The IDSA guideline on CAP concluded that PCT cannot be used in the decision to start or withhold antibiotics in patients with CAP 1

PCT Diagnostic Performance

• PCT has better diagnostic accuracy than CRP for sepsis diagnosis:
  • PCT: sensitivity 0.80, specificity 0.77, area under curve 0.85 1
  • CRP: sensitivity 0.80, specificity 0.61, area under curve 0.73 1
• However, PCT should not be used as the sole criterion for initiating antibiotics

Recommended PCT-Guided Algorithm

1. Initial Assessment:

   • Perform clinical evaluation to determine pretest probability of bacterial infection
   • Order PCT measurement along with other relevant tests

2. Interpretation of PCT Results:

   • PCT <0.1 μg/L: Very low likelihood of bacterial infection
   • PCT 0.1-0.25 μg/L: Low likelihood of bacterial infection
   • PCT 0.25-0.5 μg/L: Possible bacterial infection
   • PCT >0.5 μg/L: High likelihood of bacterial infection

3. Decision Making:

   • DO NOT use PCT alone to withhold initial antibiotics in patients with high clinical suspicion of infection 1
   • For patients already on antibiotics, consider discontinuation if:
     • PCT decreases by ≥80% from peak value, OR
     • PCT <0.5 μg/L and clinical improvement 1
   • Monitor PCT levels every 24-48 hours in critically ill patients to guide therapy duration

Important Caveats and Limitations

• PCT should always be used as a complementary tool to clinical assessment, not as a standalone test 1
• PCT sensitivity for bacterial infection ranges from 38-91%, underscoring that this test alone cannot justify withholding antibiotics 1
• PCT may be elevated in non-infectious conditions (trauma, surgery, severe shock)
• PCT has limited value in immunocompromised patients, as most trials excluded these populations 1
• The cost of PCT assays and availability of reproducible, high-sensitivity tests may limit implementation 2

Conclusion

PCT has demonstrated value primarily for antibiotic de-escalation and discontinuation rather than for initial treatment decisions. The strongest evidence supports its use in respiratory infections and critical care settings. While PCT-guided algorithms can safely reduce antibiotic exposure, they should always be used in conjunction with thorough clinical assessment and not as the sole criterion for antibiotic management decisions.