Maxime Verhoeven

217 Gender difference in OST-scores in RA patients and controls and hand volume (estimate 0.03, 95%CI 0.01 to 0.05, indicating higher OST-scores with more hand volume). In our opinion, not all of these results are easy to explain. To exclude a system error of the HandScan device, although the manufacturer assured sex is no factor in the algorithm to calculate the OST-score, we aimed to perform an additional study in which a HandScan measurement is performed twice within the same participant; it is already known that the test-retest reliability, based on two measurements, is good on the patient-level. 3 However, due to the COVID-19 pandemic, it was not feasible to perform this study yet. In summary, OST-scores in controls and probably also in RA patients are statistically significantly higher in males compared to in females, although there is considerable overlap in OST-scores between subgroups. This suggests that the HandScan cannot be used for the diagnosis of RA, and has drawbacks when comparing disease activity between groups of female and male RA-patients in research. The gender difference, which has to be analysed further, plays no role however when repeated OST-scores, whether or not integrated in an index, are used in individual RA patients, to evaluate in clinical practice their disease activity over time. 2,4 Figure Distribution of OST-scores in subgroups, a single score for each individual. Control females, n= 45; Control males, n= 30; RA females, n= 2200; RA males, n= 1157. RA= rheumatoid arthritis; OST= optical spectral transmission, score range 0 – 66 (=worst). 12