Serum calprotectin correlates with risk and disease severity of ankylosing spondylitis and its change during first month might predict favorable response to treatment.

To investigate the association of serum calprotectin with risk and severity of ankylosing spondylitis (AS), and to study its value for predicting treatment responses. 262 AS patients and 260 health controls (HCs) were enrolled in this study. 142 active AS patients were treated by pharmaceutical therapy and clinical response was evaluated according to ASAS 40 improvement criteria. 4 ml blood sample was collected from AS patients and HCs at enrollment, and from 142 active AS patients at month 1, 3 and 6 after treatments. And, serum calprotectin, IL-1β, IL-17 and TNF-α expressions were assessed by Enzyme-linked immune sorbent assay (ELISA). The expression of calprotectin in AS patients was remarkably higher compared to HCs, and Receiver Operating Curve (ROC) analysis showed that baseline calprotectin was of great diagnostic value for AS. Calprotectin level was positively correlated with CRP, ESR, PGA, pain VAS, BASDAI and BASFI scores, moreover, patients with higher calprotectin levels were with elevated expressions of IL-1β, IL-17 and TNF-α. Post-treatment, the calprotectin levels of active AS patients notably decreased from baseline to 1, 3 or 6 month. Additionally, patients achieved ASAS 40 were with more considerable change in calprotectin level during first month, and change of calprotectin during first month could predict patients achieving ASAS 40 with AUC of 0.691. Serum calprotectin level could be a promising biomarker for risk and severity of AS, and change of calprotectin during first month post-treatment might predict more favorable treatment response in active AS patients.