Multibiomarker disease activity score and C-reactive protein in a cross-sectional observational study of patients with rheumatoid arthritis with and without concomitant fibromyalgia

Abstract

Objectives: To examine the association between a multibiomarker disease activity (MBDA) score, CRP and clinical disease activity measures among RA patients with and without concomitant FM.

Methods: In an observational cohort of patients with established RA, we performed a cross-sectional analysis comparing MBDA scores with CRP by rank correlation and cross-classification. MBDA scores, CRP and clinical measures of disease activity were compared between patients with RA alone and RA with concomitant FM (RA and FM) by univariate and multivariate analyses.

Results: CRP was ⩽1.0 mg/dl for 184 of 198 patients (93%). MBDA scores correlated with CRP (r = 0.755, P < 0.001), but were often discordant, being moderate or high for 19%, 55% and 87% of patients with CRP ⩽0.1, 0.1 to ⩽0.3, or 0.3 to ⩽1.0 mg/dl, respectively. Among patients with CRP ⩽1.0 mg/dl, swollen joint count (SJC) increased linearly across levels of MBDA score, both with (P = 0.021) and without (P = 0.004) adjustment for CRP, whereas CRP was not associated with SJC. The 28-joint-DAS-CRP, other composite measures, and their non-joint-count component measures were significantly greater for patients with RA and FM (n = 25) versus RA alone (n = 173) (all P ⩽ 0.005). MBDA scores and CRP were similar between groups.

Conclusion: MBDA scores frequently indicated RA disease activity when CRP did not. Neither one was significantly greater among patients with RA and FM versus RA alone. Thus, MBDA score may be a useful objective measure for identifying RA patients with active inflammation when CRP is low (⩽1.0 mg/dl), including RA patients with concomitant FM.

Keywords: C-reactive protein; RAPID3; biomarkers; disease activity; fibromyalgia; multibiomarker; rheumatoid arthritis.

Fig. 1

Scatter plot of multibiomarker disease activity scores and CRP values Linear regression line is shown for 198 patients: 25 with RA and FM (closed circles) and 173 with RA alone (open circles). Spearman rank correlation coefficients were r = 0.755 for all 198 patients; r = 0.890 for patients with RA and FM; and r = 0.734 for patients with RA alone (all P < 0.001). MBDA: multibiomarker disease activity.

Fig. 2

Swollen joint counts as a function of multibiomarker disease activity score SJC are shown for RA patients with CRP ≤1 mg/dl (N = 184), stratified by categories of MBDA score: low (<30), moderate (30–44) and high (>44). Boxes represent IQR. Whiskers extend to the most extreme observed value within 1.5 times the IQR from the median. Horizontal lines within boxes represent medians. Diamonds represent means. SJC increased linearly across the levels of MBDA score (P = 0.021), controlling for CRP in multivariate negative binomial regression analysis with ordinal scores for MBDA score and CRP [32]. MBDA: multibiomarker disease activity; SJC: swollen joint count; IQR: interquartile range.