Procalcitonin for the early discrimination of fever etiology in patients with systemic autoimmune diseases attending the emergency department

In febrile patients with known systemic autoimmune disease, early discrimination between infection and disease flare often represents a clinical challenge. This study aimed at evaluating the efficacy of procalcitonin (PCT) and other common inflammatory biomarkers in discriminating disease flare from bacterial infections in the Emergency Department (ED). In a cross-sectional observational retrospective study, we identified consecutive febrile patients with a known diagnosis of systemic autoimmune disease, admitted to the ED, and subsequently hospitalized. Flare vs infective disease was defined on clinical records at hospital discharge. Dosage of common inflammatory markers was performed at ED admission. Out of 177 patients, those with infection were most commonly elderly, frail, and with reduced peripheral oxygen saturation at admission. When compared to C-reactive protein (CRP) and white blood count (WBC), PCT showed the best performance in discriminating infections vs flare. However, only at a very high threshold value of 2 ng/ml, the PCT had a satisfactory negative predictive value of 88.9%, although with a very low specificity of 13.6% and a positive predictive value of 35.8%. Our data suggest that in the ED setting, the early PCT determination has low accuracy in the differentiation of disease flare from infection in patients with known rheumatologic disease. However, the PCT could be useful in elderly and comorbid subjects, in supporting clinical assessment and in recognizing those febrile patients needing prompt antibiotic treatment.