Maxime Verhoeven

192 Chapter 10 Table 2 Developed DAS-OST formulae using DAS28-ESR as reference.* Developed index Formula Explained variance of model (%) Optimal cut-off for Boolean remission DAS-OST -0.44 + OST-score * 0.03 + male sex * -0.11 + LN(ESR) * 0.77 + VAS * 0.03 78% 2.2 DAS-OST(JC) -0.34 + √JC-OST* 0.15 + male sex * -0.09 + LN(ESR) * 0.77 + VAS * 0.03 78% 2.0 DAS-OST without patient VAS -0.11 + OST-score * 0.04 + male sex * -0.25 + LN(ESR) * 0.88 48% 2.6 *formulae derived from development cohort (i.e., 2238 observations from MMC cohort), DAS28-ESR was used as reference in all models. OST= optical spectral transmission; ESR= erythrocyte sedimentation rate; VAS= patients’ visual analogue scale of general health; JC-OST= joint count, assessing 22 joints for inflammation, based on optical spectral transmission. Model validation Agreement Table 3 shows agreement of the different DAS-OST indices with DAS28. In line with above results DAS-OST including VAS showed higher agreement with the original DAS28-ESR compared to DAS-OST without patient VAS (ICC 0.88 and 0.82 in internal and external validation vs. 0.66 and 0.49) and measurement error was larger with DAS-OST without patient VAS (in external validation 0.87 vs. 1.28). Agreement and measurement error were similar and difference not statistically significant for models using total OST- score and JC-OST to derive DAS-OST, see Table 3 and Supplementary Figure S1-6. Table 3 Agreement of DAS-OST indices with DAS28 and measurement error in internal and external validation cohort. Validation cohort Developed index Measurement error Agreement (ICC (95%CI)) Internal DAS-OST 0.58 0.88 (0.87 – 0.90) DAS-OST(JC) 0.58 0.88 (0.87 – 0.89) DAS-OST without patient VAS 0.90 0.66 (0.62 – 0.69) External DAS-OST 0.87 0.82 (0.75 – 0.86) DAS-OST(JC) 0.87 0.81 (0.75 – 0.86) DAS-OST without patient VAS 1.28 0.49 (0.36 – 0.60) Internal validation cohort consisted of 1120 observations from MMC cohort, not used in development cohort. External validation cohort consisted of 151 observations from the ACURA cohort. DAS-OST consisted of total OST-score, gender, ESR and VAS; DAS-OST(JC) consisted of √JC-OST, gender, ESR and VAS; DAS-OST without patient VAS consisted of total OST-score, gender and ESR. ICC= random two-way mixed effect intra-class correlation coefficient; CI= confidence interval.