Validation of the Synovo Digital Disease Activity Score (DDAS) Against Physician-Performed DAS28/CDAI: A Non-Clinical, Non-Interventional, Non-Academic Study

Rheumatoid arthritis is a chronic inflammatory disease that can lead to pain, functional impairment, joint damage and disability. Evidence from tight-control and treat-to-target studies shows that structured and repeated measurement of disease activity, followed by timely clinical action, improves disease control and remission outcomes.

The Synovo DDAS combines patient-reported information with movement features derived from four guided smartphone videos. The system produces a continuous score calibrated to the DAS28 scale. The study evaluates the measured relationship between DDAS and clinician-derived DAS28. It does not assume interchangeability and does not test autonomous treatment decisions.

The study is designed to determine whether the DDAS demonstrates sufficient association, agreement and longitudinal tracking to justify further independent and multicenter validation. This is an exploratory, single-centre study intended to establish an initial clinical evidence base rather than definitive clinical interchangeability or regulatory-grade performance.

Primary objective: To assess the association between paired DDAS and clinician-derived DAS28 values.

Secondary objectives

• To quantify numerical agreement between DDAS and clinician-derived DAS28 using mean bias and limits of agreement, with appropriate adjustment for repeated measurements within participants.
• To assess score scaling and agreement using regression analysis and a linear mixed-effects model with a participant-level random intercept.
• To evaluate categorical agreement across the standard DAS28 disease activity bands using a confusion matrix and quadratic-weighted Cohen's kappa.
• To estimate sensitivity, specificity, positive predictive value and negative predictive value at clinically relevant DAS28 thresholds, including high disease activity, treatment target and remission.
• To assess the ability of DDAS to track the direction and magnitude of changes in clinician-derived DAS28 across repeat routine-care visits.

Inclusion criteria

• Age 18 years or older
• Any sex or gender
• Clinician-confirmed rheumatoid arthritis, consistent with established ACR/EULAR criteria or a documented routine-care diagnosis
• Receiving routine care at Aap Ka Clinic during the study period
• Able and willing to provide written informed consent
• Able to complete the DDAS assessment independently or with reasonable non-clinical assistance
• Access to a compatible smartphone or tablet and sufficient connectivity for video upload

Exclusion criteria

• Younger than 18 years
• Unable to provide informed consent
• A non-rheumatoid condition that substantially prevents completion or interpretation of the guided movements
• Unable to complete study procedures despite reasonable assistance
• Concurrent participation in another interventional study where participation could affect the reference or index assessments