What does elevated procalcitonin (PCT) indicate?

From the Guidelines

Elevated procalcitonin (PCT) levels typically indicate a bacterial infection, particularly a severe systemic infection like sepsis, with levels above 0.5 ng/mL suggesting possible bacterial infection, and levels exceeding 2.0 ng/mL strongly indicating sepsis or severe bacterial infection. Procalcitonin is a protein that increases dramatically during bacterial infections but remains relatively low during viral infections or non-infectious inflammatory conditions 1. Normal procalcitonin levels are below 0.1 ng/mL.

Key Points to Consider

• Procalcitonin is particularly useful for guiding antibiotic therapy decisions, as rising levels may indicate the need to start antibiotics, while falling levels suggest effective treatment or that antibiotics might be safely discontinued 1.
• The test is valuable because it can help distinguish between bacterial and viral infections, potentially reducing unnecessary antibiotic use.
• However, procalcitonin should always be interpreted alongside clinical symptoms, other laboratory findings, and the patient's overall condition, as certain non-infectious conditions like trauma, surgery, or certain cancers can also cause elevated levels 1.
• Recent studies have shown that PCT may be elevated during severe viral illness, including influenza and COVID-19, potentially making its discriminating power for predicting the causative microorganisms less useful 1.

Clinical Application

• In ICU patients with suspected sepsis, clinicians should not initially withhold antibiotics, but PCT levels of less than 0.5 µg/L or levels that decrease by greater than or equal to 80% from peak levels may guide antibiotic discontinuation once patients stabilize 1.
• PCT-guided antibiotic treatment in ICU patients with infection and sepsis patients has been shown to result in improved survival and lower antibiotic treatment duration 1.
• Measuring PCT in critically ill patients with a new fever and no clear focus of infection with low to intermediate clinical probability of bacterial infection is recommended in addition to bedside clinical evaluation, but not in patients with high clinical probability of bacterial infection 1.

From the Research

Elevated Procalcitonin (PCT) Indications

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

• Bacterial infections, particularly sepsis 2, 3, 4, 5, 6
• Inflammatory responses to bacterial toxins and cytokines 3
• Renal involvement in pediatric urinary tract infections 2
• Secondary inflammations 2
• Non-bacterial diseases such as malaria, severe trauma, burns, and medullary carcinoma of the thyroid 5

Procalcitonin as a Diagnostic Marker

PCT is considered a promising diagnostic marker for sepsis and antibiotic therapy due to its:

• Rapid elevation in response to bacterial infections 2, 5
• Correlation with the severity of illness 2
• Ability to differentiate between bacterial and viral infections, although not always effective 2, 4
• Utility in monitoring response to antimicrobial therapy 2, 3, 4

Clinical Applications of Procalcitonin

PCT has several clinical applications, including:

• Guiding antimicrobial therapy in special patient populations, such as those with renal dysfunction, cardiac compromise, or immunocompromised states 3
• Diagnosing bacterial infections and guiding antibiotic treatment in patients with respiratory illness 4
• Monitoring the resolution of infection and guiding decisions regarding early termination of antibiotic treatment 4
• Predicting outcomes in patients with sepsis, although the optimal cut-offs for starting or discontinuing antibiotic treatment are uncertain 6