Procalcitonin, white blood cell count and C-reactive protein as predictors of S. aureus infection and mortality in infective endocarditis

Background: Infective endocarditis (IE) is characterized by high rates of in-hospital death, and Staphylococcus aureus infection predicts a worse prognosis. We aimed to assess if admission inflammatory biomarkers (white blood cell – WBC – count, C-reactive protein — CRP, and procalcitonin) are informative on microbiological etiology and short-term outcomes. Methods: Data from 236 patients admitted for IE from January 2013 to June 2018 were retrieved from a multicenter registry. Results: Fifty-two patients (22%) were infected by S. aureus. WBC, CRP and procalcitonin had area under the curve (AUC) values for S. aureus infection of 0.595, 0.675, and 0.727, respectively. Adding procalcitonin to WBC improved discrimination over WBC alone (p = 0.045), and procalcitonin predicted S. aureus infection independently from the other inflammatory biomarkers and patient characteristics. Patients with WBC ≥ 12,800/mm3, CRP ≥ 130 mg/L, and procalcitonin ≥ 1.7 ng/mL had an almost 20-fold higher risk of S. aureus infection than patients with all biomarkers < cut-offs. AUC values for in-hospital death were 0.702, 0.725 and 0.727 for the WBC, CRP, and procalcitonin, respectively. Among inflammatory biomarkers, WBC and procalcitonin independently predicted in-hospital death. Procalcitonin refined risk stratification when added to WBC, and to the combination of WBC and CRP. Patients with WBC ≥ 10,535/mm3, CRP ≥ 85 mg/dL, and procalcitonin ≥ 0.4 ng/mL had a 27-fold higher risk of in-hospital death than patients with all biomarkers < cut-offs. Conclusions: Among patients with IE, high levels of inflammatory biomarkers on admission, particularly procalcitonin, are associated with a higher likelihood of S. aureus infection, and a higher risk of in-hospital mortality.