Responsiveness of the core set, response criteria, and utilities in early rheumatoid arthritis

Objective-Validation of responsiveness and discriminative power of the Worl d Health Organisation/International League of Associations for Rheumatology (WHO/ ILAR) core set, the American College of Rheumatology (ACR), and Euro pean League for Rheumatology (EULAR) criteria for improvement/response, and other single and combined measures (indices) in a trial in patients with e arly rheumatoid arthritis (RA). Methods-Ranking of measures by response (standardised response means and ef fect sizes) and between-group discrimination (unpaired t test and chi (2) v alues) at two time points in the COBRA study. This study included 155 patie nts with early RA randomly allocated to two treatment groups with distinct levels of expected response: combined treatment, high response; sulfasalazi ne treatment, moderate response. Results-At week 16, standardised response means of core set measures ranged between 0.8 and 3.5 for combined treatment and between 0.4 and 1.2 for sul fasalazine treatment (95% confidence interval +/-0.25). Performance of pati ent oriented measures (for example, pain, global assessment) was best when the questions were focused on the disease. The most responsive single measu re was the patient's assessment of change in disease activity; at 3.5. Pati ent utility, a generic health status measure, was moderately (rating scale) to poorly (standard gamble) responsive. Response means of most indices (co mbined measures) exceeded 2.0, the simple count of core set measures improv ed by 20% was most responsive at 4.1. Discrimination performance yielded si milar but not identical results: best discrimination between treatment grou ps was achieved by the EULAR response and ACR improvement criteria (at 20% and other percentage levels), the pooled index, and the disease activity sc ore (DAS), but also by the Health Assessment Questionnaire (HAQ) and grip s trength. Conclusions-Responsiveness and discrimination between levels of response ar e not identical concepts, and need separate study. The WHO/ILAR core set co mprises responsive measures that discriminate well between different levels of response in early RA. However, the performance of patient oriented meas ures is highly dependent on their format. The excellent performance of indi ces such as the ACR improvement and EULAR response criteria confirms that t hey are the preferred primary end point in RA clinical trials.