Objective: The plasma levels of calprotectin, a major S100 leukocyte protein, is cross-sectionally associated to clinical and laboratory markers of inflammation and to radiographic damage in rheumatoid arthritis (RA). High amounts of calprotectin are found in synovial fluid from RA patients. Our objective was to examine if calprotectin could be an independent predictor of joint destruction over time.
Methods: A total of 124 RA patients were assessed at baseline and after 10 years with inflammatory markers (calprotectin, CRP, ESR), serological variables (anti-CCP, IgA and IgM RF) and radiographic and clinical assessments of joint damage (hand radiographs and Rheumatoid Arthritis Articular Damage (RAAD) score). Progression of radiographic damage was assessed according to van der Heijde modified Sharp score.
Results: The highest calprotectin levels were at both examinations found in patients positive for anti-CCP, IgA and IgM RF (p<0.001). Calprotectin had moderate to good correlations with inflammatory and serological markers (r=0.41-0.67, p<0.001). Patients with normal baseline calprotectin levels had lower degree of joint damage (p<0.001). High univariate associations were found between baseline calprotectin levels and progression in Sharp Score (p=0.007) as well as RAAD score (p=0.003). Baseline calprotectin was independently associated with progression in Sharp Score (p=0.045) and with the RAAD score (p=0.012) in multiple linear regression analyses including baseline levels of CRP, ESR, anti-CCP in addition to demographic variables.
Conclusion: Calprotectin was an independent predictor of clinical and radiographic joint damage after 10 years. These findings support that calprotectin may be a prognostic biomarker for erosive disease in patients with RA.