Is pre-assessment for anti-TNF therapy in RA necessary in the UK? Analysis of DAS28 in six centres

Different wording of the Patient Global Visual Analogue Scale (PG-VAS) affects rheumatoid arthritis patients' scoring and the overall Disease Activity Score (DAS28): a cross-sectional study

OBJECTIVE

The Disease Activity Score in 28 joints (DAS28) is a key measure in clinical practice and clinical trials. There are at least five different versions of the 'Patient Global' Visual Analogue Scale (PG-VAS) being used in the DAS28. The developers suggested that the PG-VAS can be an assessment of global health or disease activity, but did not specify the wording of the question. There is no consensus on what the PG-VAS is intended to capture, and the different words and phrases have not been evaluated. The aim of this study was to test if phrasing affects PG-VAS scores and hence yields different results for the DAS28.

METHODS

Fifty patients with rheumatoid arthritis taking biologic agents in a rheumatology outpatient department completed a self-administered questionnaire containing five versions of the 100 mm PG-VAS.

RESULTS

All PG-VAS versions correlated strongly with each other (rho = 0.67-0.87, p < 0.0001). However, individual scores for each PG-VAS, when compared with the comparator on a Bland-Altman chart had wide limits of agreement--the largest being -42 mm to +45 mm. The five overall DAS28 scores were calculated for each patient using the five different PG-VAS. The largest difference in DAS28 scores was 0.63.

CONCLUSION

Different phrasing of the PG-VAS gives different DAS28 results. As the DAS28 is a key outcome measure, such differences have the potential to influence clinical decisions relating to eligibility for biologic agents and evaluation of new therapies. We urgently need to decide on the concept to be measured and the phrasing required to capture this. The PG-VAS phrasing should then be standardized and validated.

DAS28 and Rheumatoid Arthritis: The Need for Standardization

Disease Activity Score in 28 Joints (DAS28) scoring in rheumatoid arthritis (RA) is now recommended as a basis for clinical decisions about treatment initiation and alteration. The British Society of Rheumatology suggests that most RA patients should have a DAS28 assessment at every clinic visit, to monitor disease activity and the impact of therapy. Establishing an accurate baseline assessment of DAS28, with regular re-evaluation, is considered crucial, so that progress towards a defined target of remission (or low disease activity) can be measured. The Treat-to-Target initiative, launched in March 2010, is now impacting on clinical practice throughout the UK and Europe. One of its key recommendations is that patients should be regularly monitored using validated composite measures of disease activity that include joint assessments. DAS28 is recommended as one of the most useful of these methods but, although it is becoming more widely adopted and training is ongoing, supported by materials produced by the European League Against Rheumatism (EULAR), the variability inherent in the four components of DAS28 means that standardization of practice methods is now an important issue. This short report details some of the pitfalls that can occur when applying DAS28 in clinical practice and suggests some workable solutions to enable departments to set up their own standard operating procedure.