What does elevated procalcitonin (PCT) indicate?

From the Guidelines

Elevated procalcitonin levels strongly indicate a bacterial infection, particularly sepsis, and should prompt immediate initiation of broad-spectrum antibiotics and further diagnostic workup. The most recent and highest quality study, published in 2021 1, suggests that procalcitonin levels can be used to support the diagnosis of bacterial infection in patients with COVID-19, and that elevated levels are associated with an increased risk of bacterial co-infection.

Key Points to Consider

• Procalcitonin is a useful marker for distinguishing bacterial from viral infections, with levels typically rising rapidly in response to bacterial endotoxins and inflammatory cytokines 1.
• A procalcitonin level of <0.1 mg/L may indicate a high likelihood of viral infection, whereas levels >0.25 mg/L may indicate a high likelihood of bacterial pneumonia 1.
• However, the sensitivity and specificity of procalcitonin for detecting bacterial infection can vary, and clinical judgment should always supersede biomarker results in decision-making 1.
• The 2017 Surviving Sepsis Campaign guidelines suggest that measurement of procalcitonin levels can be used to support shortening the duration of antimicrobial therapy in sepsis patients, and to support the discontinuation of empiric antibiotics in patients who initially appeared to have sepsis but subsequently have limited clinical evidence of infection 1.

Recommendations

1. Start broad-spectrum antibiotics without delay in patients with elevated procalcitonin levels and suspected bacterial infection, considering a combination like piperacillin-tazobactam 4.5g IV every 6 hours plus vancomycin 15-20 mg/kg IV every 8-12 hours (adjusted based on renal function).
2. Obtain blood cultures before starting antibiotics, if possible, but do not delay treatment.
3. Assess for signs of organ dysfunction and initiate supportive care as needed (e.g., IV fluids, vasopressors, oxygen).
4. Identify and control the source of infection (e.g., drain abscesses, remove infected devices).
5. Monitor procalcitonin levels every 24-48 hours to assess treatment response and guide antibiotic duration.
6. Consider discontinuing antibiotics when procalcitonin decreases by 80% from its peak or falls below 0.5 ng/mL.

From the Research

Elevated Procalcitonin (PCT) Indications

Elevated procalcitonin (PCT) levels are associated with several clinical indications, including:

• Bacterial infections, as opposed to viral infections 2, 3, 4, 5, 6
• Severity of disease, with higher levels indicating more severe illness 2, 4
• Sepsis and septic shock, with PCT levels correlating with the severity of sepsis 2, 4, 6
• Infection characteristics, such as the site of infection, microbial agent, and presence of bacteremia 4
• Organ dysfunction, with PCT levels correlating with the degree of end-organ dysfunction 4

Clinical Utility of PCT

The clinical utility of PCT lies in its ability to:

• Guide antibiotic treatment, with PCT-guided antibiotic stewardship reducing antibiotic exposure and associated side effects 3, 5, 6
• Differentiate between bacterial and non-bacterial infections, particularly in respiratory illness 3, 4
• Monitor the resolution of infection and guide decisions regarding early termination of antibiotic treatment 3, 5
• Provide invaluable information when viewed as one piece of a clinical puzzle, taking into account preexisting comorbid conditions and clinical scenarios 4, 5