Calprotectin reflects inflammatory and autoantibody burden in RA

Design

Cross-sectional cohort with central biomarker and autoantibody measurement

Population

4,521 Scandinavian patients with rheumatoid arthritis

Primary outcome

Association of plasma calprotectin with clinical activity and autoantibodies

Effect

Calprotectin correlated with ESR (0.53) and CRP (0.47); independently tracked autoantibody load

CRP and ESR are the routine inflammation markers in rheumatoid arthritis, but they do not capture everything. This cross-sectional study measured plasma calprotectin — a marker of neutrophil activity — in 4,521 Scandinavian patients and related it to clinical activity and autoantibodies.

Calprotectin correlated with ESR, CRP, swollen and tender joint counts and pain. Patients with both high CRP and high calprotectin (14% of the cohort) had more active disease than those with high CRP alone. Independent of CRP, raised calprotectin was linked to a higher load of anti-modified protein autoantibodies, including anti-CCP2, and the association strengthened with the breadth of the autoantibody response, especially alongside rheumatoid factor.

The signal is that calprotectin captures a dimension of disease — combined inflammatory and autoantibody burden — that CRP misses, which could help characterise the harder-to-control seropositive patient. This is cross-sectional, so it is a marker worth understanding rather than a test proven to change management.

• Cross-sectional study of 4,521 patients with rheumatoid arthritis.
• Calprotectin correlated with ESR, CRP, swollen and tender joint counts and pain.
• Patients high in both CRP and calprotectin (14%) had more active disease than those high in CRP alone.
• Raised calprotectin, independent of CRP, tracked higher anti-modified protein autoantibody load.
• Treat it as a research marker of combined burden, not yet a test to guide treatment.

Why it matters

It points to a marker that may flag the seropositive, high-autoantibody patient whose burden CRP understates.

Don't overread it

This was cross-sectional; it characterises what calprotectin reflects, not that measuring it changes management.

The statistics, in plain English

Moderate correlations (around 0.5 with ESR, 0.47 with CRP) mean calprotectin overlaps with but is not identical to standard markers; as a cross-sectional study it shows association, not that acting on calprotectin improves outcomes.

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