Comparison of procalcitonin and C-reactive protein as markers of sepsis

OBJECTIVE: To compare the clinical informative value of procalcitonin (PCT) and C-reactive protein (CRP) plasma concentrations in the detection of infection and sepsis and in the assessment of severity of sepsis. DESIGN: Prospective study. SETTING: Medicosurgical intensive care unit. PATIENTS: Seventy consecutive adult patients who were admitted to the intensive care unit for an expected stay >24 hrs. INTERVENTIONS: None. MEASUREMENTS: PCT and CRP plasma concentrations were measured daily during the intensive care unit stay. Each patient was examined daily for signs and symptoms of infection and was classified daily in one of the following four categories according to the American College of Chest Physicians/Society of Critical Care Medicine criteria: negative, systemic inflammatory response syndrome, localized infection, and sepsis group (sepsis, severe sepsis, or septic shock). The severity of sepsis-related organ failure was assessed by the sepsis-related organ failure assessment score. MAIN RESULTS: A total of 800 patient days were classified into the four categories. The median plasma PCT concentrations in noninfected (systemic inflammatory response syndrome) and localized-infection patient days were 0.4 and 1.4 ng/mL (p <.0001), respectively; the median CRP plasma concentrations were 79.9 and 85.3 mg/L (p =.08), respectively. The area under the receiver operating characteristic curve was 0.756 for PCT (95% confidence interval [CI], 0.675-0.836), compared with 0.580 for CRP (95% CI, 0.488-0.672) (p <.01). The median plasma PCT concentrations in nonseptic (systemic inflammatory response syndrome) and septic (sepsis, severe sepsis, or septic shock) patient days were 0.4 and 3.65 ng/mL (p <.0001), respectively, whereas those for CRP were 79.9 and 115.6 mg/L (p <.0001), respectively. The area under the receiver operating characteristic curve was 0.925 for PCT (95% CI, 0.899-0.952), compared with 0.677 for CRP (95% CI, 0.622-0.733) (p <.0001). The linear correlation between PCT plasma concentrations and the four categories was much stronger than in the case of CRP (Spearman's rho, 0.73 vs. 0.41; p <.05). A rise in sepsis-related organ failure assessment score was related to a higher median value of PCT but not CRP. CONCLUSION: PCT is a better marker of sepsis than CRP. The course of PCT shows a closer correlation than that of CRP with the severity of infection and organ dysfunction.