could improve outcomes.16–23 While no single biomarker has been found to capture the complex biology of the disease, a multi-biomarker score that captures the complex interactions and numerous biological pathways in RA could improve the assessment and tracking of disease activity. A multi-biomarker disease activity (MBDA) test has been developed that simulta- neously measures serum levels of 12 proteins shown to be asso- ciated with RA disease activity in multiple studies and combines them into a score between 1 and 100.24 25 The purpose of the current study was to evaluate a broad set of serum biomarkers of RA disease activity and to evaluate the performance of the MBDA score as an instrument of disease activity in early RA patients from the CAMERA study. PATIENT AND METHODS Patient cohort Serum samples were studied from the CAMERA cohort, a 2-year, multicentre, prospective, open-label study.6 7 26 Patients with early RA who met the 1987 revised American College of Rheumatology criteria for RA27 and were 16 years of age or more were ran- domly assigned to either an intensive or conventional treatment strategy. Patients were initially treated with MTX alone. If MTX caused toxicity or was ineffective at the maximum dose of 30 mg/ week, cyclosporine was added. Non-steroidal anti-inﬂammatory drugs were allowed. Oral glucocorticoids were not allowed but intra-articular were permitted if necessary. Every month (in the intensive treatment strategy) or every 3 months (conventional treatment strategy), the following clinical variables were assessed: SJC and TJC including 28 joints (SJC28 and TJC28, respectively), VAS pain (0–100 mm; 100=worst possible pain), VAS-GH (0–100 mm; 100=worst score), ESR (mm/h1st), CRP (mg/l) and morning stiffness (0–180 min). In the conventional strategy group, dose adjustments were made based on the opinion of the individual rheumatologist. In the intensive strategy group, dose adjust- ments were made based on changes in joint counts, ESR and the VAS-GH, as assessed using a computer decision program.7 The DAS28,9 an index for disease activity, was calculated based on TJC28, SJC28, ESR (or CRP) and VAS-GH. Annual radiographs of hands and feet were evaluated for Sharp/van der Heijde score by two readers, blinded for treat- ment strategy and clinical information, but not sequence. The median yearly progression rate was calculated for the period 0–2 years. Serum sampling and laboratory methods A total of 120 serum samples from the CAMERA study were examined; of these, 72 were collected at baseline (39 from inten- sive strategy) and 48 were collected at 6 months (31 from inten- sive strategy). Although serum was only available for a subset of study subjects and these subjects had slightly lower baseline joint counts than the overall cohort, otherwise they were very representative and had similar clinical outcomes (supplementary table 1). Serum was collected in standard separator tubes accord- ing to the manufacturer’s protocol, frozen as soon as possible after blood collection, and stored at −20°C until analysis. The concentrations of 20 serum protein biomarkers (calpro- tectin, C-C motif chemokine ligand 22, CRP, epidermal growth factor, inter-cellular adhesion molecule 1, interleukin (IL)-1 beta, IL-1 receptor antagonist, IL-6, IL-6 receptor, IL-8, leptin, matrix metallopeptidase 1, matrix metallopeptidase 3, pyridinoline, resistin, serum amyloid A, tumour necrosis factor receptor type I, vascular cell adhesion molecule 1, vascular endothelial growth factor A and cartilage glycoprotein 39 (YKL-40)) were measured Ann Rheum Dis 2012;71:1692–1697. doi:10.1136/annrheumdis-2011-200963 annrheumdis-2011-200963.indd 2 Clinical and epidemiological research by customised immunoassays (Sector Imager 6000 (Meso Scale Discovery, Gaithersburg, Maryland, USA) or individual ELISA; supplementary table 2). The reagents used were designed to block interference from RF and other heterophilic antibodies.24 MBDA score A disease activity algorithm using 12 of the serum protein biomarkers (ﬁgure 1) was applied to calculate MBDA scores. Biomarkers were selected (from 130 candidates) in prior studies by a combination of objective regression modelling and assay performance criteria.25 The assays and algorithm were the same as those used in the previously developed and validated MBDA test, Vectra DA (Crescendo Bioscience, South San Francisco, California, USA). This algorithm used serum biomarker concen- trations to separately estimate TJC28, SJC28 and VAS-GH. The estimates for TJC28, SJC28 and VAS-GH were combined with a CRP test result to calculate an overall MBDA score: a whole number ranging from 1 to 100, using a formula analogous to that of the DAS28-CRP (ﬁgure 1).The algorithm was previously developed and trained using independent serum samples from the Index for Rheumatoid Arthritis Measurement (n=512) and Brigham and Women’s Rheumatoid Arthritis Sequential Study (n=167) observational cohort studies.29 Since the MBDA score is calculated using a formula similar to that of the DAS28-CRP, it is straightforward to calculate the MBDA score equivalent to a given DAS28-CRP value (by multiplying the DAS28-CRP by 10.53 and adding 1). Thresholds were deﬁned by calculating the MBDA score values equivalent to established DAS28-CRP thresholds separating low, moderate and high disease activity.30 The result- ing thresholds deﬁned MBDA scores ≤25 as remission, 26–29 as low, 30–44 as moderate and >44 as high disease activity. Statistical analysis Except where speciﬁed, analyses used data from all samples. The associations between individual biomarker concentrations (log-transformed to approach a normal distribution) and disease activity (DAS28-CRP, SJC28, TJC28 and VAS-GH) were assessed Figure 1. MBDA score algorithm The MBDA score algorithm uses the same equation as the DAS28-CRP, with biomarkers used to predict the Swollen Joint Count (SJC28), Tender Joint Count (TJC28), and general health (VAS-GH) components of the equation. (PTJC= predicted TJC, PSJC= predicted SJC; PVAS-GH= predicted VAS-GH). The Venn diagram lists the MBDA score biomarkers used to predict each MBDA score component. This algorithm provides an MBDA score between 1 and 100. 1693 8/23/2012 3:34:17 AM