Maxime Verhoeven

191 Development and validation of DAS-OST Table 1 Patients’ demographics and clinical data of the Máxima MC (MMC) and ACURA cohort. MMC cohort MMC cohort development MMC cohort internal validation ACURA cohort external validation Patients’ demographics Number of patients, 1505 1272 817 151 Female, n (%) 979 (65) 831 (65) 541 (66) 100 (67) Age (year), mean (SD) 65.1 (12.0) 64.9 (12.2) 65.6 (11.6) 60.5 (13.1) duration of RA (year), mean (SD) 11.4 (8.3) 11.3 (8.4) 11.7 (8.2) 5.9 (8.0) Seropositivity, n (%) 1068 (71) 901 (72) 588 (73) 116 (77) Clinical data Number of observations 3358 2238 1120 151 DAS28, mean (SD) 2.5 (1.3) 2.5 (1.3) 2.5 (1.2) 3.8 (1.6) ESR (mm/hr), median (IQR) 9 (5 – 21) 9 (5 – 21) 9 (5 – 21) 18 (10 – 34) SJC28, median (IQR) 0 (0 – 2) 0 (0 – 2) 0 (0 – 2) 1 (0 – 4) TJC28, median (IQR) 0 (0 – 2) 0 (0 – 2) 0 (0 – 2) 2 (0 – 8) patient VAS, median (IQR) 30 (10 – 50) 30 (10 – 50) 28 (10 – 50) 40 (20 – 65) OST-score, mean (SD) 12.6 (5.0) 12.7 (5.1) 12.6 (5.0) 15.0 (6.1) SD= standard deviation; Seropositivity= presence of rheumatoid factor and/or anti-cyclic citrullinated peptide antibodies; IQR= interquartile range; DAS28= disease activity score assessing 28 joints; ESR= erythrocyte sedimentation rate; SJC28= swollen joint count assessing 28 joints; TJC28= tender joint count assessing 28 joints; VAS= visual analogue scale of general health, range 0-100=worst; OST = optical spectral transmission, score range 0-66=worst. Model development The derived formulae for the different DAS-OST indices are shown in Table 2. Next to ESR and VAS, gender was found to influence DAS28-ESR, independently fromOST-score. None of the variables modified the association between OST-score and DAS28. The model without patient VAS had a markedly lower explained variance (i.e., 48% vs. 78% in models with VAS). The analysis on the association between joint specific OST-scores and presence of swelling showed that it was not possible to establish one cut-off for all joints, therefore cut-offs were established per individual joint to calculate a JC-OST, see Supplementary Table S1. This JC-OST was subsequently used to derive a DAS-OST(JC) formula, see Table 2. 10