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 patients with systemic antineutrophil cytoplasmic antibody-associated vasculitis (AAV) clinical disease activity was assessed by score systems. Infection was defined by clinical and microbiological means. PCT was determined in parallel with concentrations of neopterin, interleukin-6 (IL-6), and C-reactive protein (CRP) in 397 serum samples.
Results: Only in 3 of the 324 samples taken from patients with autoimmune disease but without concomitant infection, serum PCT levels were above the normal range (>0.5 ng/ml), whereas neopterin, CRP and IL-6 were elevated in patients with active underlying disease. All systemic infections (N=16 in 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.