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Use of a "critical difference" statistical criterion improves the predictive utility of the Health Assessment Questionnaire-Disability Index score in patients with rheumatoid arthritis

: Behrens, F.; Koehm, M.; Schwaneck, E.C.; Schmalzing, M.; Gnann, H.; Greger, G.; Tony, H.-P.; Burkhardt, H.

Fulltext ()

BMC Rheumatology 3 (2019), Art. 51, 9 pp.
ISSN: 2520-1026
Journal Article, Electronic Publication
Fraunhofer IME ()

The Health Assessment Questionnaire-Disability Index (HAQ-DI) is used to assess functional status in rheumatoid arthritis (RA), but the change required for meaningful improvements remains unclear. A minimum clinically important difference (MCID) of 0.22 is frequently used in RA trials. The aim of this study was to determine a statistically defined critical difference for HAQ-DI (HAQ-DI-dcrit) and evaluate its association with therapeutic outcomes.
We retrospectively analyzed data from adult German patients with RA enrolled in a multicenter observational trial in which they received adalimumab therapy at the decision of the treating clinician during routine clinical care. The HAQ-DI-dcrit, defined as the minimum change that can be reliably discriminated from random long-term variations in patients on stable therapy, was determined by evaluating intra-individual variation in patient scores. Other outcomes of interest included Disease Activity Score-28 joints and patient-reported pain and fatigue.
The HAQ-DI-dcrit was calculated as an improvement (decrease) from baseline of 0.68 in a discovery cohort (N = 1645) of RA patients on stable therapy and with moderate disease activity (mean DAS28 [standard deviation] of 4.4 [1.6]). In the full patient cohort (N = 2740), 22.1% of patients achieved a HAQ-DI-dcrit improvement at month 6. Compared with patients with a small improvement in HAQ-DI (decrease of ≥0.22 to < 0.68) or no improvement (< 0.22), patients achieving a HAQ-DI-dcrit at month 6 had better therapeutic outcomes at months 12 and 24, including stable functional improvements. Change in pain was the most important predictor of HAQ-DI improvement during the first 6 months of therapy.
A HAQ-DI-dcrit of 0.68 is a reliable measure of functional improvement. This measure may be useful in routine clinical care and clinical trials.