Maxime Verhoeven

209 DAS28 vs. DAS-OST; rheumatologist’s clinical classification For DAS28-based LDA classification, sensitivity and specificity were 87% and 72%, respectively and for DAS-OST-based LDA, these values were 81% and 59%, respectively, all versus the clinical reference. Lower values were obtained for both indices when using remission instead of LDA, see supplementary Table S1. Optimal cut-offs for inactive disease according OST-scores were ≤16.36 and ≤10.64 for males and females, respectively. Sensitivity and specificity for males were 66% and 50%, respectively, and 53% and 63%, respectively, for females, see supplementary Table S1. In line with the outcomes above, agreement (Cohen’s kappa/Gwet’s AC1) of the clinical classification with DAS28-based classification was higher compared with DAS-OST (0.41/0.55 and 0.54/0.76 vs. 0.24/0.37 and 0.36/0.64 for remission and LDA, respectively), see supplementary Table S1. DISCUSSION To our knowledge this is the first study that identifies the value of a disease activitymeasure with a HandScan score replacing joint counts to classify RA as active versus inactive, with as reference standard the rheumatologist’s clinical classification. DAS-OST showed amoderate performance (AU-ROC 0.78), but statistically significantly less, compared to DAS28. The performance of OST-score alone was poor, in line with earlier published data, 8,11 indicating that the OST-score has to be combined with other parameters into an index. As expected, more favourable outcomes were obtained for DAS28-based LDA than for DAS-OST-based LDA. False negatives, as well as false positives were more often observed for DAS-OST than for DAS28 (4/20 vs. 2/20 and 2/20 vs. 1/20, respectively). Similarly, strength of agreement of the rheumatologist’s classification with DAS28-based classification was moderate, and it was modest with DAS-OST. This limits the potential clinical applicability of DAS-OST. As a face-to-face visit with the rheumatologist is not required for DAS-OST, which saves time and cost, it would be efficient to select patients having no LDA based on DAS-OST for a face-to-face visit with the rheumatologist, assuming that most of those patients have active disease. In this setting, a higher specificity of DAS- OST (thus low number of patients with missed active RA) would preferable over a high sensitivity, because at the visit, false classifications of RA as active can be corrected. Cost might also be saved when using DAS-OST compared to DAS28, as healthcare workers/ rheumatologists should be trained to perform joint count assessment as objective as possible. 3 Of course, the HandScan machine has to be purchased. The difference for males and females in optimal cut-off of OST-score for inactive disease is remarkable. Our previous study, 8 as well as the current study show that OST- scores were higher in males than in females. A plausible explanation is the difference in size and volume of hands between men and women. 12 A limitation of our study is that our reference, i.e., rheumatologist’s clinical classification as active or inactive RA, probably is partly dependent of DAS28, as this 11