Procalcitonin for discrimination between activity of systemic autoimmune disease and systemic bacterial infection

Objective:To investigate whether serum procalcitonin (PCT) levels could be useful to differentiate between systemic infection and the activity of the underlying disease in autoimmune disease. Methods: In 18 patients with systemic lupus erythematodes (SLE) and 35 pati ents with systemic antineutrophil cytoplasmic antibody-associated vasculiti s (AAV) clinical disease activity was assessed by score systems. Infection was defined by clinical and microbiological means. PCT was determined in pa rallel with concentrations of neopterin, interleukin-6 (IL-6), and C-reacti ve protein (CRP) in 397 serum samples. Results: Only in 3 of the 324 samples taken from patients with autoimmune d isease but without concomitant infection, serum PCT levels were above the n ormal range (> 0.5 ng/ml), whereas neopterin, CRP and IL-6 were elevated in patients with active underlying disease. All systemic infections (N = 16 i n AAV-patients) were associated with markedly elevated PCT-levels (mean +/- SD:1.93 +/- 1.19 ng/ml). Conclusion: PCT may serve as a useful marker for the detection of systemic bacterial infection in patients with autoimmune disease.