Background Calprotectin, mainly secreted by neutrophils and monocytes in the condition of inflammation, has been found elevated in many autoimmune disease patients. However, there has been no study focusing on calprotectin in antiphospholipid antibodies (aPLs) positive patients. In this study, we aimed to identify the clinical associations of calprotectin in aPLs positive patients.
Methods Consecutive patients with persistent aPLs positivity (detected at least 12 weeks apart) referred to Peking Union Medical College Hospital and age, sex-matched health controls (HCs) were included. Clinical data and aPLs profile of patients were collected. Serum calprotectin was measured using Enzyme-linked immunosorbent assay (ELISA) (Elabscience). The cutoff value was defined as mean + 2 standard deviation (SD) of HCs.
Results A total of 467 patients were included in the study. The median age was 34.74 [30.28, 42.50] years old, and 77.3% were female. 38 HCs were included in the study. The median age was 35.00 [32.75, 39.00] years old, and 78.9% were female. Serum calprotectin in aPLs positive patients was much higher than it in HCs (484.62±149.37 ng/ml) regardless of systemic lupus erythematosus (SLE) (p<0.001). Patients without SLE (640.98±259.96 ng/ml) had relative lower serum calprotectin than patients with SLE (690.49±268.22 ng/ml) (p=0.047, figure 1). The cutoff was set as 783.36 ng/ml. 93 patients (19.9%) were positive for calprotectin. The positivity of calprotectin was significantly associated with SLE (p=0.044), microangiopathy (p=0.046), non-vascular neurological manifestations (p=0.047), and lupus anticoagulant (LA) positivity (p=0.017). Livedo reticularis may also have association with calprotectin (p=0.099, table 1).
Conclusions Serum calprotectin elevates in aPLs positive patients, and could be a novel marker of microangiopathy in antiphospholipid syndrome patients. More studies are required to explore the association between calprotectin and microangiopathy in APS patients, as well as the clinical application value of calprotectin in the future.
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