Table 2 Agreement between classiﬁcation of disease activity (low, moderate and high) according to the MBDA score and DAS28-CRP MBDA score L w o Moderate High κ (95% CI) Weighted κ (95% CI) DAS28-CRP Baseline visit Low 0 1 0 8 0 15 0.23 (−0.03 to 0.48) 0.20 (0.01 to 0.39) Heijde (SHS) score over 2 years (progression >0 SHS units) as dependent variable. Multivariate (logistic) analyses adding other well-known prognostic factors for progression of joint dam- age (RF and baseline joint damage) were also performed (with treatment strategy, age and gender as covariates) to investigate the additional prognostic value of the MBDA score and DAS28- CRP. Separate analyses were performed for the MBDA score and DAS28-CRP at baseline and 6 months. The statistical software packages R and SPSS V.15.0 were used for data analysis. Except where otherwise noted, a p value <0.05 was considered to be statistically signiﬁcant. RESULTS Association with clinical disease activity Of the 20 proteins biomarkers examined, 14 were statistically sig- niﬁcantly correlated with DAS28-CRP, 11 with DAS28, 11 with SJC, nine with TJC and six with VAS-GH (with a false discovery rate <0.05). Pearson correlations between the individual biomark- ers and several disease activity measures are presented in table 1. The MBDA score was calculated using 12 of the 20 biomark- ers (Patient and Methods section and ﬁgure 1) and compared with DAS28-CRP, a widely accepted conventional measure of disease activity. Similar results were observed for DAS28 (data not shown). Figure 2A illustrates that the MBDA score achieved a statistically signiﬁcant correlation to the DAS28-CRP (r=0.72; p<0.001). The MBDA score distinguished between remission/ low disease activity and moderate/high disease activity with an AUROC of 0.86 (p<0.001, ﬁgure 2A,B). The prespeciﬁed AUROC analysis was conducted using a DAS28-CRP cut-off of 2.7, and it was noted that more subjects had high disease activity than low disease activity using this cut-off. To assess the impact of imbalance in the sizes of the disease activity groups upon clas- siﬁcation performance, the AUROC was also calculated using a cut-off equal to the median DAS28-CRP of 4.6. The resulting AUROC was 0.83, very similar to the AUROC obtained using the prespeciﬁed cut-off of 2.7. Similar results were obtained using only a single visit per patient (data not shown). The κ for agreement between the MBDA score and DAS28- CRP for classiﬁcation of the disease activity level was 0.34 (95% CI 0.19 to 0.49). For baseline visits alone, κ was 0.23 (95% CI −0.027 to 0.48); this was 0.32 (95% CI 0.11 to 0.53) for 6-month visits alone. Weighted κ results were similar (table 2). Clinical and epidemiological research High 2 4 10 Combination (baseline and 6 months) Low Moderate 9 4 7 15 2 19 0.34 (0.19 to 0.49) 0.41 (0.21 to 0.61) High 5 9 50 Figure 3. MBDA scores by treatment arm and time point For each treatment strategy (i.e. intensive tight control MTX-based and conventional MTX-based treatment strategy) the results of the MBDA score are shown at baseline and after 6 months of treatment. Only results of patients with MBDA score at baseline and 6 months are shown. biomarkers were combined together as in the MBDA score, but with CRP left out. When included in a multivariate model for DAS28-CRP (overall r2=0.52), these other MBDA biomarkers were independently associated with disease activity (p<0.001) and CRP was not (p=0.09). Similar results were obtained with multivariate models for the clinical components of DAS28: the other 11 MBDA biomarkers were independently associated with SJC28 (p<0.001), TJC28 (p<0.01) and VAS-GH (p=0.02), and CRP was not (p=0.35, p=0.81 and p=0.68, respectively). Tracking response to therapy In response to the treatment as used in the CAMERA study (n=46), the mean (SD) MBDA score dropped from 53 (18) at baseline to 39 (16) at the 6-month visit (p<0.0001; ﬁgure 3). The intensive and conventional strategy groups were also consid- ered separately, revealing a signiﬁcant decrease in MBDA score in the intensive strategy group (n=31) from 53 (17) to 35 (14) (p<0.0001). In the conventional strategy group (n=15), the mean MBDA score decreased from 55 (20) to 46 (19) (p=0.07). Moderate Moderate High 3 5 40 6-Month visit Low 9 3 7 7 2 4 0.32 (0.11 to 0.53) 0.39 (0.02 to 0.76) Counts indicate the number of patients in each disease activity category. Low, MBDA score ≤29, DAS28-CRP ≤2.7; moderate, MBDA score 30–44, DAS28-CRP 2.7–4.1; high, MBDA score >44, DAS28-CRP >4.1. MBDA, multi-biomarker disease activity; DAS28-CRP, disease activity score based on 28 joints-C reactive protein. Contribution of non-CRP biomarkers Since the MBDA score uses CRP, which is a commonly avail- able laboratory test, we used multivariate regression to examine whether the other biomarkers in the score were independently associated with disease activity in the presence of CRP. The other Radiographic progression The MBDA score and DAS28-CRP were examined for their ability to predict radiographic progression after 2 years of treat- ment. For one and ﬁve patients, respectively, no radiographs were available at baseline and 2 years. The median (IQR) yearly Ann Rheum Dis 2012;71:1692–1697. doi:10.1136/annrheumdis-2011-200963 annrheumdis-2011-200963.indd 4 1695 8/23/2012 3:34:18 AM