Influence of obesity, age, and comorbidities on the multi-biomarker disease activity test in rheumatoid arthritis.

INTRODUCTION: Traditional markers of inflammation are often required for inclusion in rheumatoid arthritis trials, yet patients with active disease may have normal lab tests. The potential use of the multi-biomarker disease activity (MBDA) test in this setting is unclear, as is understanding of whether it is influenced by patient characteristics (e.g., age, BMI, and comorbidities).

METHODS: Using data from the Corrona registry, we conducted a cross-sectional analysis of RA patients with MBDA tests. Patients were classified as low (<30), moderate (30-44, and high (>44) and by clinical and RA-related factors. Regression was used to evaluate the association between MBDA score and age, body mass index, comorbidities, and RA-related factors.

RESULTS: Of 357 eligible patients, 76% (n = 273) had normal CRP (<10mg/L) with high (33%), moderate (45%), and low (22%) disease activity by MBDA. The MBDA score was significantly associated with BMI, age, CDAI, and SJC. There was no association between MBDA score and fibromyalgia, diabetes, smoking, or COPD; none were confounders between MBDA score and either SJC or CDAI. For patients in CDAI remission, older age (2.6 units per decade; p = 0.03) and obesity (β = 10.5 for BMI > 30, referent to <25; p = 0.02) were independently associated with MBDA score. An adjusted MBDA score was proposed that was highly correlated with the original MBDA (r = 0.91).

CONCLUSION: In this real-world analysis, the MBDA score was associated with RA disease activity, obesity, and age, and was negligibly affected by common comorbidities. Almost one-third of patients with normal CRP had high MBDA scores. An adjustment to the MBDA score to account for body mass index and age is proposed.