What is the specificity of procalcitonin (PCT) for infection?

From the Guidelines

Specificity of Procalcitonin (PCT) for Infection

The specificity of procalcitonin (PCT) for infection is 0.77 (95% CI, 0.60–0.88), indicating a moderate degree of value for diagnosing sepsis in adult patients 1.

Key Points

• PCT is a precursor hormone of calcitonin that discriminates the systemic response due to bacterial causes from viral and noninfectious etiologies.
• PCT levels begin to rise four hours after exposure to bacteria, reaching a maximum level after six to eight hours, and decrease rapidly after antibiotic treatment.
• The diagnostic accuracy of PCT for sepsis has a sensitivity of 0.80 (95% CI, 0.69–0.87) and a specificity of 0.77 (95% CI, 0.60–0.88), with a diagnostics odd ratio (DOR) of 12.50 (95% CI, 3.65–42.80) 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.
• However, the use of PCT testing to guide antibiotics treatment in COVID-19 patients is confounded by the hyperinflammatory status or cytokine storm induced by SARS-CoV-2 infection, which may result in a higher PCT production than in other viral pneumonia 1.

Clinical Application

• 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.
• A low PCT level at initial presentation has a high negative predictive value to rule out bacterial coinfections, while an initially high PCT level did not provide additional value to traditional clinical criteria or laboratory data 1.

From the Research

Specificity of Procalcitonin for Infection

• The specificity of procalcitonin (PCT) for infection is a topic of ongoing research, with studies suggesting that PCT is a powerful biomarker for bacterial infection 2.
• PCT has been shown to be more specific for sepsis and bacterial infection compared to other biomarkers such as CRP 3.
• However, the specificity of PCT for bacterial coinfection in patients with respiratory viral illness has been found to be lower than previously thought, with a specificity of 61% after matching for severity 4.
• PCT levels have been found to be elevated in patients with severe viral infection, and are not suppressed by interferon signalling, suggesting that PCT is a better indicator of disease severity than bacterial coinfection 4.
• The utility of PCT assessment in special patient populations, such as those with renal dysfunction or immunocompromised states, is less clear, and higher thresholds for diagnosing infection or de-escalating therapy may be necessary 5.

Factors Affecting PCT Specificity

• The clinical situation, including the pretest probability for bacterial infection, acuity and severity of presentation, and PCT test results, can affect the specificity of PCT for infection 6.
• Patient-specific factors, such as underlying disease states and concomitant therapies, can also affect the interpretation of PCT results 5.
• The optimal threshold for diagnosing infection or de-escalating therapy in special populations is unclear, and PCT levels should be considered along with clinical criteria 5.

Clinical Applications

• PCT-guided antibiotic stewardship has been shown to reduce antibiotic exposure and associated side-effects among patients with respiratory infection and sepsis 6.
• PCT measurement may have a role in guiding de-escalation of antibiotic therapy in special populations, but should be used in conjunction with clinical criteria 5.