A recent study published in May of ‘Arthritis Research & Therapy’ confirmed about the relationship of serum calprotectin levels with disease activity in both rheumatoid arthritis (RA) and axial spondyloarthritis (axSpA), except in psoriatic arthritis (PsA).

Calprotectin or S100A8/S100A9 protein is recognized as a damage-associated molecular pattern protein and indicates primarily neutrophil activation. Matthias Jarlborg et al. examined whether the serum calprotectin is associated with disease activity and severity in RA, axSpA, and PsA.

On the whole, 1729 patients were included from the Swiss Clinical Quality Management (SCQM) registry. Out of these, 969 were RA patients, 451 were axSpA patients and 237 were PsA patients. And, 72 asymptomatic first-degree relatives of patients with RA were regarded as healthy controls (HC). Their serum calprotectin was calculated. Different outcomes were used for the 3 rheumatic diseases as:

• RA patients: Swollen joint count (SJC), Disease Activity Score (DAS), Health Assessment questionnaire (HAQ), joint radiographs, and ultrasound power Doppler (USPD) was used;
• AxSpA patients: Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Ankylosing Spondylitis Disease Activity Score (ASDAS) and coxitis; and
• PsA patients: SJC and Disease Activity Index for PSoriatic Arthritis (DAPSA)

The Kruskal-Wallis tests were used to compare the outcomes by calprotectin quartile levels for continuous outcomes or trend tests for categorical outcomes.

As found, in every disease group, the median levels of serum calprotectin were higher than HC. All the clinical outcomes were found to be statistically different amongst quartiles of serum calprotectin, demonstrating a possible link between calprotectin levels and higher disease activity (SJC, DAS, and USPD scores) and severity (joint radiographs and HAQ). An association between the levels of calprotectin and ASDAS score and occurrence of coxitis was revealed in axSpA. The SJC and DAPSA did not vary across calprotectin quartiles for PsA patients.