What is the interpretation of Procalcitonin (PCT) levels?

From the Guidelines

Procalcitonin (PCT) levels should be interpreted based on their concentration in the blood, with levels below 0.1 ng/mL suggesting absence of significant bacterial infection, levels between 0.1-0.5 ng/mL indicating low probability, and levels above 2.0 ng/mL strongly suggesting severe bacterial infection or sepsis, as supported by the most recent guidelines 1. When interpreting PCT levels, it is essential to consider the clinical context and other laboratory findings, as certain conditions like trauma, surgery, and some cancers can elevate PCT independently of bacterial infection.

• A PCT level below 0.1 ng/mL suggests absence of significant bacterial infection.
• Levels between 0.1-0.5 ng/mL indicate low probability of bacterial infection.
• Moderate bacterial infection risk is associated with levels between 0.5-2.0 ng/mL.
• Levels above 2.0 ng/mL strongly suggest severe bacterial infection or sepsis. For patients with suspected sepsis, antibiotics should be started immediately if PCT is above 0.5 ng/mL, while levels below this threshold may allow for watchful waiting in stable patients, as recommended by the Surviving Sepsis Campaign guidelines 1. Serial measurements of PCT are valuable, as declining PCT levels (ideally by more than 80% from peak) indicate effective treatment and may support antibiotic discontinuation, as suggested by the Society of Critical Care Medicine and the Infectious Diseases Society of America guidelines 1. It is crucial to note that PCT should always be interpreted alongside clinical assessment and other laboratory findings, as certain conditions can elevate PCT independently of bacterial infection, and the use of PCT levels to guide antibiotic therapy decisions should be based on the most recent and highest-quality evidence available 1.

From the Research

Interpreting Procalcitonin Levels

To interpret procalcitonin (PCT) levels, it is essential to consider the clinical context and the cutoff values established by various studies. The following points summarize the key aspects of interpreting PCT levels:

• PCT is a biomarker that can help differentiate bacterial from non-bacterial infections and inflammation states, particularly in respiratory illness 2.
• Low PCT levels can help rule out bacterial infection in patients with low pretest probability for bacterial infection and low-risk general condition 2.
• In high-risk individuals and/or high pretest probability for infection, empiric antibiotic treatment is mandatory, and subsequent monitoring of PCT can help track the resolution of infection and guide decisions regarding early termination of antibiotic treatment 2.
• A cutoff value of 0.25 μg/L in non-ICU patients or 0.5 μg/L in ICU patients seems appropriate for making decisions about the initiation and discontinuation of antibiotic therapy 3.
• In patients with a significantly elevated baseline PCT level, a subsequent drop of >80% appears to be reasonable for discontinuing antibiotics 3.
• The optimal and most widely used PCT cut-off value is 0.5 ng/mL, with a corresponding sensitivity of 76% and specificity of 69% for diagnosing bacteraemia 4.
• Low PCT levels can be used to rule out the presence of bacteraemia, especially in intensive-care patients, where the area under the SROC curve was found to be 0.88 4.
• The appropriate cutoff values of PCT for bacteremia were 0.38 microg/L for the high negative predictive value and 0.83 microg/L for the high positive predictive value 5.

Clinical Considerations

When interpreting PCT levels, clinicians should consider the following factors:

• The clinical situation, including the pretest probability for bacterial infection 2.
• The acuity and severity of presentation 2.
• The patient's underlying condition, such as immunocompromised or neutropenic status 4.
• The combination of PCT with other diagnostic tools, such as blood culture and PCR, to increase the sensitivity for mortality 5.