OBJECTIVE: Achieving targeted disease activity (DA) is the primary therapeutic strategy in RA. Point measurements of DA are done at out-patient visits, however true DA between visits remains unobserved. This study sought to describe and validate a new outcome measure, i.e. time in remission (TIR). METHODS: Patients were enrolled in the Czech ATTRA-RA registry. TIR was calculated using linear interpolation of the DAS28-ESR determined at outpatient visits. Correlation coefficients were computed between TIR and DAS28-CRP, HAQ, Simple Disease Activity Index (SDAI), patient global assessment (PGA) and physician global assessment (PhGA). Using logistic regression, TIR was used as a predictor of remission (SDAI ≤3.3) and non-disability (HAQ <0.5). The predictive value of TIR was compared with point and sustained remission using the cross-validated area under receiver-operating curves. RESULTS: Since 2010, 2618 RA patients started anti-TNF therapy and were followed until 2020 or until treatment discontinuation. During the first 6 months of therapy, 56% of patients had no remission (TIR = 0), and 22% of patients reached sustained remission (TIR = 1), while 22% of patients had point remissions with 0 < TIR < 1. EULAR good responders and moderate/non-responders spent 64 ± 42% and 6 ± 18% of time in remission, respectively. The mean TIR grew during the follow-up and was correlated with DAS28-CRP, SDAI, HAQ, PGA, and PhGA (P < 0.0001). TIR at 3 and 6 months predicted remission (SDAI ≤3.3) and non-disability (HAQ <0.5) at 13 and 19 months better than point or sustained remission. CONCLUSIONS: TIR is an intuitive way of estimating unobserved DA between scheduled visits; its calculation only requires two consecutive DA values (https://www.medevio.cz/tir-calculator/). TIR is a valid predictor of RA outcomes.

1st Faculty of Medicine Charles University Prague

Department of Pharmacology Faculty of Medicine Masaryk University Brno Czech Republic

Institute of Biostatistics and Analyses Ltd Spinoff Company of the Faculty of Medicine of the Masaryk University Brno

Institute of Health Economics and Technology Assessment

Institute of Rheumatology Prague

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