What is the use of procalcitonin?

Procalcitonin: Clinical Utility and Applications

Procalcitonin (PCT) is a biomarker primarily used to distinguish bacterial infections from viral or non-infectious causes and to guide antibiotic therapy decisions, with its greatest utility in respiratory infections and sepsis management. 1

What is Procalcitonin?

• PCT is a peptide precursor of calcitonin that rises rapidly in bacterial infections
• Normal values in healthy individuals: <0.05 ng/mL 1
• Results typically available within one hour using point-of-care testing or routine laboratory methods 1

Clinical Interpretation of PCT Levels

PCT Level	Clinical Interpretation
<0.1 ng/mL	High probability of viral infection or non-infectious condition
0.1-0.25 ng/mL	Low probability of bacterial infection
0.25-0.5 ng/mL	Possible bacterial infection
>0.5 ng/mL	High probability of bacterial infection
>2.0 ng/mL	High probability of sepsis or severe bacterial infection

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Key Clinical Applications

1. Respiratory Tract Infections

• Lower Respiratory Tract Infections (LRTI): European Society of Clinical Microbiology and Infectious Diseases suggests using PCT to guide antibiotic initiation for patients with suspected LRTI likely to be admitted to hospital (weak recommendation, moderate evidence) 2
• Acute Exacerbation of Asthma: Suggested for guiding antibiotic initiation in patients likely to be hospitalized (weak recommendation, low evidence) 2
• Acute Exacerbation of COPD: Suggested for guiding antibiotic initiation in patients likely to be hospitalized (weak recommendation, moderate evidence) 2
• Not recommended for patients with dyspnea and suspected/known heart disease 2

2. Sepsis Management

• PCT can be used to guide antibiotic discontinuation in sepsis patients 1
• Serial measurements showing decreasing levels (≥80% from peak or to <0.25 ng/mL) can support safe antibiotic discontinuation 1

3. COVID-19 Pneumonia

• A low PCT value early in confirmed COVID-19 illness may guide withholding or early stopping of antibiotics, especially in less severe disease 2
• PCT may be elevated in COVID-19 due to inflammatory activation rather than bacterial co-infection 2

Advantages Over Other Biomarkers

PCT offers several advantages over C-reactive protein (CRP):

• Faster response: Rises 4 hours after bacterial exposure (vs. 12-24 hours for CRP)
• Better diagnostic accuracy: Higher specificity for bacterial infections
• Quicker normalization: Returns to normal more rapidly, allowing better monitoring of disease progression 1, 3

Impact on Antibiotic Stewardship

• PCT-guided therapy can significantly reduce antibiotic exposure in hospitalized patients 1, 4
• In primary care and emergency settings, PCT guidance can reduce initial antibiotic prescriptions by 30-80% for mild respiratory infections 5
• In hospitalized patients with community-acquired pneumonia and sepsis, PCT guidance can reduce antibiotic duration by 25-65% 5

Important Limitations and Caveats

• Not a standalone test: PCT should always be interpreted within clinical context 4
• Not recommended based on fever alone: Weak recommendation against using PCT based solely on fever to guide antibiotic initiation 2
• No perfect threshold: No PCT threshold perfectly distinguishes viral from bacterial pneumonia 2
• Protocol adherence issues: Adherence to PCT-guided protocols can be challenging, limiting widespread adoption 6
• Assay quality matters: Only highly sensitive PCT assays should be used in clinical practice 5

Best Practice Approach

1. Assess clinical situation with focus on pretest probability for bacterial infection
2. Consider patient's risk status and severity of presentation
3. Interpret PCT results in this context
4. For low-risk patients with low PCT: Consider withholding antibiotics
5. For high-risk patients or high pretest probability: Start empiric antibiotics regardless of PCT
6. Use serial PCT measurements to guide antibiotic discontinuation when levels decrease significantly

Remember that decisions on initiating, altering, or discontinuing antimicrobial therapy should never be made solely based on PCT values but should incorporate regular clinical assessment 6.