Serum Calprotectin in Rheumatoid Arthritis: A Promising Diagnostic Marker, How Far Is It Related to Activity and Sonographic Findings?

Background: In the past 2 decades, there has been increasing interest in calprotectin. It is released and detected in serum and body fluids as a potentially useful clinical inflammatory marker. The protein has been described in synovial tissue in rheumatoid arthritis (RA) patients, specifically in the lining layer adjacent to the cartilage-pannus junction, which is the primary site of cartilage destruction and bone erosion. Assessment of inflammatory activity in RA is of pivotal importance for the optimal treatment. Our aim in this study is to measure the serum calprotectin levels in RA patients and to assess its association-if there is any-with disease activity score and radiological findings using the musculoskeletal ultrasound.

Patients And Methods: In our case control study, we included 44 RA patients (Group I) and 20 age- and sex-matched healthy volunteers who served as the control group (Group II). Both groups were subjected to full history taking and thorough clinical examination. Assessment of RA disease activity state was done for all RA patients using the Disease Activity Score 28. Laboratory investigations included the measurement of complete blood cell count, erythrocyte sedimentation rate, C-reactive protein, rheumatoid factor, anticitrullinated peptide antibodies, kidney, liver functions; serum calprotectin levels were determined using enzyme-linked immunosorbent assay and radiological joint assessment was done using musculoskeletal ultrasound score.

Results: There was a statistically significant elevation of serum calprotectin levels among RA patients when compared with healthy controls. Statistically significant correlations were also found between serum calprotectin and the ultrasound grading score, Disease Activity Score 28, and erythrocyte sedimentation rate, which reflect the degree of inflammatory activity in the affected joints in RA patients. Moreover, the study yielded a significant correlation between serum calprotectin levels and rheumatoid autoantibodies (rheumatoid factor and anticitrulli-nated peptide antibodies), which are strong predictors of the aggressiveness of the disease. Serum calprotectin at a cutoff level of 93.9 μg/dL had 88.6% sensitivity and 100% specificity for diagnosis of RA.

Conclusion: Calprotectin was found to have high association with laboratory and ultrasonography markers of inflammation in RA patients, so it is recommended for use as a marker of inflammatory activity in RA patients especially for the follow-up of patients on biological therapy to assess its efficacy.