Construct validation of the ACR 1991 revised criteria for global functional status in rheumatoid arthritis

In order to assess the construct and discriminatory validity of the 1991 ACR functional status criteria for rheumatoid arthritis (RA), a cross-sectional analysis of 62 consecutive patients with RA (according to the American Rheumatism Association 1987 revised criteria) who were attending the outpatient clinic of rheumatology, University Hospital Zürich, was carried out. A moderate-to-strong association of the ACR criteria with pain (r = 0.54), the tender (r = 0.54) and swollen joint count (r = 0.31), grip strength (r = -0.49), C-reactive protein (r = 0.35), the HAQ disability index (r = 0.76), self-perceived global health (r = 0.58), and the Larsen radiological score (r = 0.32) was found. The mean scores of most disease parameters and all 8 domains of the health assessment questionnaire were significantly different between, and increased regularly across, the 4 classes. We conclude that the ACR 1991 functional status criteria for RA are a valid measure of the consequences of impairment and discriminate well the physical functional status.