From the Guidelines
An elevated procalcitonin (PCT) level primarily indicates a bacterial infection, particularly systemic infections like sepsis or severe bacterial pneumonia. PCT is a precursor to the hormone calcitonin that rises significantly during bacterial infections but typically remains low during viral infections or non-infectious inflammatory conditions. The degree of elevation often correlates with infection severity, with levels above 0.5 ng/mL suggesting possible bacterial infection and levels exceeding 2 ng/mL strongly indicating sepsis or severe infection. PCT is especially useful in critical care settings to guide antibiotic therapy decisions, as rising levels may indicate worsening infection while declining levels suggest effective treatment. However, interpretation requires clinical context, as certain conditions like major trauma, surgery, or some cancers can cause non-infectious PCT elevations. PCT measurements are most valuable when tracked over time rather than as single readings, helping clinicians monitor infection progression and treatment response, as supported by recent studies such as 1. Key points to consider include:
- PCT levels can help differentiate between bacterial and viral infections, with higher levels indicating bacterial infections 1.
- Serial PCT measurements can aid in the early detection of secondary bacterial infections in critically ill patients, particularly those with COVID-19 1.
- PCT-guided antibiotic stewardship has been shown to reduce antibiotic usage and improve patient outcomes in certain clinical settings 1.
- The use of PCT as a biomarker for infection should always be considered in conjunction with clinical judgment and other diagnostic tools 1.
From the Research
Elevated Procalcitonin Levels
Elevated procalcitonin (PCT) levels can indicate several conditions, including:
- Bacterial infections, such as sepsis caused by intestinal infection 2
- Medullary thyroid cancer metastases, which can synthesize PCT, leading to elevated levels 3
- Bacterial meningitis, with PCT levels being a useful marker for distinguishing bacterial from abacterial meningitis 4
Diagnostic Potential
PCT has been shown to be a useful marker for:
- Diagnosing bacterial infections in the peri-operative period 5
- Monitoring surgical high-risk patients 5
- Distinguishing bacterial from abacterial meningitis, with high specificity but potential false-negative results 4
Factors Affecting Procalcitonin Levels
- Renal dysfunction can affect the accuracy of PCT for diagnosing postoperative infection, with different thresholds recommended for patients with impaired renal function 6
- Non-infectious causes of inflammation, such as auto-immune or allergic disorders, do not significantly increase PCT levels 5
Clinical Implications
- Elevated PCT levels can indicate a bacterial origin with high specificity, but false-negative results can occur 4
- Persistently elevated or increasing PCT levels after 2 days can be associated with an unfavorable clinical course 4
- PCT levels can be used to monitor the severity of infection and sepsis, and to guide antibiotic therapy 2, 5