Background Treat-to-target is the standard of care in rheumatoid arthritis (RA). Integral to this is the regular assessment of disease activity. Several tools have been developed and validated to allow patients with RA to self-assess disease activity. One of these tools is the Patient-derived Disease Activity Score (PDAS). Two versions pf PDAS are available: PDAS1 and PDAS2. PDAS-2 is a composite score that includes patient global assessment of disease activity (PGA), modified health assessment questionnaire (MHAQ), patient self-assessed 28 swollen joint count (ptSJC28) and early morning stiffness score (EMS). PDAS2 correlated with DAS28ESR and Clinical Disease Activity Index (CDAI).
Objectives In order to reduce patient burden, we developed a simplified PDAS2 (sPDAS2) by removing the need to assess EMS.
Methods Data from 311 patients with established RA were analysed. The original model for calculating PDAS2 was: PDAS2 = 2.667 + [(0.021 x PGA) + (0.483 x MHAQ) + (0.033 x patient 28 SJC) + (0.002 x EMS)]. Linear regression was used to develop a sPAS2 using DAS28ESR as a dependent variable and including PGA, MHAQ and ptSJC28. R-squares were used to examine the statistical model fit of sPDAS2 compared with PDAS2. sPDAS2 was further validated using data from a different cohort of 204 patients with established RA. Correlation of sPDAS-2 with DAS28 and CDAI was examined to assess criterion and construct validity.
Results Based on data from 311 patients with RA. The following model for sPDAS2 was developed: sPDAS2 =2.447 + 0.028 x PGA + 0.422 x HAQ + 0.053 x patients 28SJC.
The R-square for PDAS2 (including EMS) was 0.601. R-square for sPDAS (without the EMS) was 0.594. A difference of 0.007 indicating minimal loss of statistical fit.
Using data from a different cohort of RA patients. sPDAS2 correlated well with DAS28ESR (r=0.72, p<0.001) and CDAI (r=0.74, p<0.001) demonstrating criterion and construct validity.
Conclusions A sPDAS2 has been developed and validated for patients with RA to self-assess disease activity. The components of sPDAS2 included PGA, mHAQ and ptSJC28 and do not require assessment of early morning stiffness.
Acknowledgement The original developed of PDAS was supported by a grant from Arthritis Research UK. The CREATE Centre is funded by Arthritis Research UK and Health and Care Research Wales.
Disclosure of Interest None declared
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