Background As the opportunities for web-based self management, support and clinical decision-making across chronic diseases increase, there is an urgent need to explore reliable means of eliciting self-reported symptoms and disease activity scores from patients with rheumatoid arthritis (RA) (1). A patient derived Disease Activity Score (DAS28), Simplified Disease Activity Index (SDAI) and Clinical Disease Activity Index (CDAI) based on self-report joint count, if reliable, could serve as an important marker of disease activity in RA. The reliability of patient self-assessment of tender and swollen joints has been examined (2), but the reliability of patient-derived scores seems to have escaped much attention.
Objectives To examine the test-retest reliability of the DAS28-CRP with three and four variables, the SDAI and the CDAI when based on patient self-assessment of tender and swollen joints, and to assess the agreement of these scores with corresponding physician derived scores in patients with RA.
Methods 30 out-clinic RA patients with stable disease were included. A joint count was performed by the patient and by an experienced physician at two visits 1 week apart. Test-retest reliability was expressed as the least significant difference (LSD = 1.96 x SD of test-retest differences), as the LSD in percent of the mean of the score (%LSD) which may be considered as the measurement error and as intra-individual coefficients of variation (CVi) = (√0.5x di2) /meani (3-5).
Results Mean age was 60±15 years, mean disease duration 15±6 years. 77% were females, 75% were erosive and 70% were sero-positive. Mean values (±SD) (visit 1) was 4.1±5.2 for TJC, 3.7±2.4 for SJC, 33±28 (0-100) for patient global assessment (GA), 22.3±21.8 (0-100) for physician GA and 7.9±6.5 for CRP (mg/l). The means of correspondingphysician and patient derived scores were nearly identical. The LSDs (%LSD) between physician and patient derived scores (visit 1) were: DAS28-CRP(4v) 0.9 (24.9), DAS28-CRP(3v) 1.0(27.8), SDAI 7.3 (51.3) and CDAI 7.3 (54.3). Similar results were found for duplicate physician and patient-derived scores. CVis for patient and physician derived scores were not significantly different for neither DAS28-CRP(3), DAS28-CRP(4), SDAI nor CDAI. CVis for SDAI and CDAI were similar but were significantly higher than for DAS28-CRP(3) and DAS28-CRP(4) (p< 0.005-0.0001). That finding applied to both intra-physician and intra-patient inter-visits agreements and to between patient and physician intra-visits agreements.
Conclusions Disease activity scores based on patient and physician reported joint counts agreed closely on group level. On the individual level, LSDs between patient and physician derived scores were considerable but corresponded to both patient and physician intra-observer LSDs. Thus, scores based on patient-performed joint counts may be an alternative to traditional physician-derived scores in patients with stable disease. More studies are needed to examine the value of patient self-assessment of disease activity scores.
Barton JL et al. J Rheumatol 2009;36:2635-41. 2) Solomon M et al. J Med Internet Res 2012;14:e32. 3) Bland JM, Altman DG. Lancet 1986;1:307-10. 4) Glüer CC et al. Osteoporos Int 1995;5:262-70. 5. Madsen OR. Spine 1996 21:2770-6.
Disclosure of Interest None Declared