Percentile benchmarks in patients with rheumatoid arthritis: Health Assessment Questionnaire as a quality indicator (QI)

Abstract

Physicians are in need of a simple objective, standardized tool to compare their patients with rheumatoid arthritis, as a group and individually, with national standards. The Disability Index of the Health Assessment Questionnaire (HAQ-DI) is a simple, robust tool that can fulfill these needs. However, use of this tool as a quality indicator (QI) is hampered by the unavailability of national reference values or benchmarks based on large, multicentric, heterogenous longitudinal patient cohorts. We utilized the 20-year longitudinal prospective data from 11 data banks of Arthritis Rheumatism and Aging Medical Information to calculate reference values for HAQ-DI. Overall, 6436 patients with rheumatoid arthritis were longitudinally followed for 32,324 person-years over the 20 years from 1981 to 2000. There were 64,647 HAQ-DI measurements, with an average of 19 measurements per person. Overall, 75% of patients were women and 89% were Caucasian; the median baseline age was 58.4 years and the median baseline HAQ-DI was 1.13. Few patients were treated with biologics. The HAQ-DI values had a Gaussian distribution except for the approximately 10% of observations showing no disability. Percentile benchmarks allow disability outcomes to be compared and contrasted between different patient populations. Reference values for the HAQ-DI, presented here numerically and graphically, can be used in clinical practice as a QI measure to track functional disability outcomes and to measure response to therapy, and by arthritis patients in self-management programs.

Figure 1

Distribution of scores on the Health Assessment Questionnaire (HAQ) Disability Index in 6436 patients (64,647 observations) with rheumatoid arthritis.

Figure 2

Percentile Health Assessment Questionnaire (HAQ) Disability Index scores plotted against disease duration for 6436 patients (64,647 observations) with rheumatoid arthritis, with 95% confidence band.

Figure 3

Percentile Health Assessment Questionnaire (HAQ) Disability Index scores plotted against disease duration for 1668 men with rheumatoid arthritis followed with 14,600 observations.

Figure 4

Percentile Health Assessment Questionnaire (HAQ) Disability Index curves plotted for 4768 women with rheumatoid arthritis with 50,047 observations.

Figure 5

Age-related changes in median Health Assessment Questionnaire Disability Index (HAQ-DI) in 64,647 observations in 6436 patients with rheumatoid arthritis compared with 5751 observations in 587 nondiseased controls of the Stanford Runners study and 23,414 observations in 2843 subjects in the University of Pennsylvania Alumni study.