Calprotectin linked to autoantibody burden and clinical measures in rheumatoid arthritis

A cross-sectional study published in Arthritis & Rheumatology examined associations between plasma calprotectin, a marker of neutrophil activity, and clinical features and autoantibodies in 4,521 Scandinavian patients with rheumatoid arthritis. Researchers centrally measured calprotectin, rheumatoid factor and anti-CCP2 isotypes, alongside antibodies to 15 citrullinated and four carbamylated or acetylated peptides. CRP and ESR were obtained from clinical measurements at blood sampling.

Calprotectin correlated with ESR (ρ=0.53), CRP (ρ=0.47), swollen joint count (ρ=0.39), tender joint count (ρ=0.26) and pain scores (ρ=0.24); all associations had p<0.0001. Patients with both elevated CRP (>10 mg/L) and calprotectin (>15 AU/ml)—613 patients, reported as 14%—had higher pain scores and swollen and tender joint counts than those with elevated CRP alone (p<0.0001), in both early and established disease.

Elevated calprotectin was associated with greater anti-modified protein autoantibody burden, including anti-CCP2, particularly when RF IgM was present. Differences across autoantibody-burden groups remained after adjustment for sex, age, RF IgM and disease duration. These findings suggest calprotectin reflects aspects of inflammation and seropositivity not fully captured by CRP alone. However, the cross-sectional design cannot establish causality or predictive value, and the abstract does not establish whether calprotectin testing improves treatment decisions or outcomes.