USEFULNESS OF PROCALCITONIN FOR DIFFERENTIATION BETWEEN ACTIVITY OF SYSTEMIC AUTOIMMUNE-DISEASE (SYSTEMIC LUPUS-ERYTHEMATOSUS SYSTEMIC ANTINEUTROPHIL CYTOPLASMIC ANTIBODY-ASSOCIATED VASCULITIS) AND INVASIVE BACTERIAL-INFECTION

Objective. To investigate whether the determination of serum procalcit onin (PCT) in systemic autoimmune disease will help to discriminate in vasive infection from highly active underlying disease. Methods. Three hundred ninety-seven serum samples, from 18 patients with systemic lu pus erythematosus (SLE) and 35 patients with systemic antineutrophil c ytoplasmic antibody-associated vasculitis (AAV), were analyzed. Clinic al disease activity was assessed by the Systemic Lupus Activity Measur e in SLE patients and by the Birmingham Vasculitis Activity Score in A AV patients. Procalcitonin concentrations were determined in parallel with concentrations of neopterin, interleukin-6 (IL-6), and C-reactive protein (CRP). Additionally, serum creatinine values were obtained. R esults. In 321 of the 324 samples from the 42 patients with autoimmune disease but without systemic infection, serum PCT levels were within the normal range (i.e., <0.5 ng/ml), whereas the values for neopterin, IL-6, and CRP were elevated in patients with active underlying diseas e. All 16 systemic infections occurred in 11 patients with AAV, and we re associated with PCT levels that were markedly elevated, to a mean /- SD of 1.93 +/- 1.19 ng/ml. No correlation between the degree of ren al impairment and PCT concentrations was seen. Conclusion. PCT may ser ve as a useful marker for the detection of systemic bacterial infectio n in patients with systemic autoimmune disease.