Objective The aim of this pilot-study was to examine serum calprotectin levels (sCAL) in patients with SLE and determine possible association with disease activity and history of vascular events.

Methods 27 consecutive SLE patients from daily hospital and outpatient rheumatology clinic and 13 healthy volunteers underwent demographic data collection, sCAL assessment (ELISA Buhlmann sCAL diagnostic test), and disease activity assessment by SLEDAI-2K for SLE patients. Patients were divided into two groups, active disease and remission, taking SLEDAI-2K value of 6 as a cut-off, and defined patients who had recent vascular incidents associated with SLE.

Results 13 patients in active group (38.5% women, median age 50 (35–58), SLE duration 8.85±6.26 years, SLEDAI-2K 14 (7–21)) were compared to 14 patients in remission group (85,7% women, median age 39 (35–53), disease duration 5.21±2.78 years, SLEDAK-2K 3.5 (2–4)) and to 13 control subjects (76,9% women, median age 25 (24–26)). Significantly higher occurrence of neuropsychiatric disease (53.8% vs. 14.3%, P=0.032) and vascular manifestations (76.9% vs. 14.3%, P=0.001) was observed in active patients compared to those in remission. We haven’t observed the difference in occurrence of APS, serositis, dermatologic, constitutional, renal, or hematologic manifestations of SLE between groups. sCAL levels were higher in all patients compared to the control group (1.1 (0.53–1.8) μg/ml vs. 0.7 (0.38–1.1) μg/ml, P=0.02). Moreover, sCAL was higher in the active group compared to remission patients (1.6 (1.1–3.0) μg/ml vs. 0.8 (0.2–1.4) μg/ml, P= 0.02). Patients with a history of recent vascular events had greater sCAL respect other SLE patients (1.7 (1.15–3) μg/ml vs. 1.0 (0.225–1.375) μg/ml, P=0.015). There was a positive correlation between SLEDAI and sCAL in all patients (ρ=0.532, P=0.0043), particularly in active ones (ρ=0.673, P=0.0017). There was no correlation between SLEDAI and sCAL within inactive patients (ρ=0.0678, P=0.818).

Conclusions SLE patients, especially those with active disease, had higher sCAL compared to healthy subjects. We established a positive correlation between vascular manifestations of SLE and sCAL, but also between SLEDAI-2K and sCAL in patients with active disease. Our study was limited due to the small sample size. Further research should confirm these hypotheses on a larger number of subjects.

Acknowledgement The authors declare no conflict of interest. This research was funded by the University of Split, School of Medicine.