What factors influence the health status of patients with rheumatoid arthritis measured by the SF-12v2 Health Survey and the Health Assessment Questionnaire?

OBJECTIVE: The Health Assessment Questionnaire Disability Index (HAQ) is a widely used outcome measure in rheumatoid arthritis (RA), whereas the SF-12v2 Health Survey (SF-12) was introduced recently. We investigated how the HAQ and SF-12 were associated with socio-demographic, lifestyle, and disease- and treatment-related factors in patients with RA.
METHODS: In RA patients from 11 Danish centers, clinical and patient-reported data, including the HAQ and SF-12, were collected. Three multiple linear regression models were estimated, with the HAQ, SF-12 physical component score (PCS), and SF-12 mental component score (MCS) as outcome and sociodemographic, lifestyle, and RA-related treatment and comorbidity characteristics as explanatory variables.
RESULTS: In total, 3156 (85%) of 3704 invited patients participated--75% women, 76% rheumatoid factor-positive, median age 61 years (range 15-93 yrs), disease duration 7 years (range 0-68 yrs), Disease Activity Score on 28 joints (DAS28) 2.97 (range 0.96-8.61), HAQ score 0.63 (range 0-3), SF-12 PCS 56 (range 6-99), and SF-12 MCS 57 (range 16-99). Variation in HAQ was associated with 12 of 15 possible variables (R(2) 0.41), in PCS and MCS with 6 of 15 variables (R(2) 0.02 and 0.05). Patients with moderate to high DAS28 and > or = 3 comorbid conditions had consistently worse HAQ and SF-12 scores compared to the reference groups, while weekly exercise was associated with better scores compared to no exercise.
CONCLUSION: The HAQ was more sensitive to differences in demographic, lifestyle, and disease- and treatment-related factors than the SF-12. The established clinical value and feasibility of the HAQ highlights its advantages over the SF-12 in describing health status in RA.