Clinically important changes in short form 36 health survey scales for use in rheumatoid arthritis clinical trials: the impact of low responsiveness.

OBJECTIVE

Despite wide use of the Short-Form 36 (SF-36) health survey in clinical trials of rheumatoid arthritis (RA), estimates of minimum clinically important improvement (MCII) for its scales are not well-established. We estimated MCIIs for SF-36 scales in patients with active RA.

METHODS

In this prospective longitudinal study, we studied 243 patients who had active RA and who completed the SF-36 before and after treatment escalation. We first assessed responsiveness with standardized response means (SRMs). For scales with adequate responsiveness (SRM ≥0.50), we used patient judgments of improvement in arthritis status as anchors for estimating MCIIs. We used receiver operating characteristic curve analysis to identify the MCIIs as the change associated with a specificity of 0.80 for improvement.

RESULTS

Patients had substantial improvement in RA activity with treatment. However, among SF-36 scales, only the physical functioning and bodily pain scales and the physical component summary had adequate responsiveness. Using 0.80 specificity for improvement as the criterion, the MCIIs were 7.1 for the physical functioning scale, 4.9 for the bodily pain scale, and 7.2 for the physical component summary.

CONCLUSION

Low responsiveness precluded estimation of valid MCIIs for many SF-36 scales in patients with RA, particularly the scales assessing mental health. Although the SF-36 has been included in many clinical trials to broaden the assessment of health status, low responsiveness limits the interpretation of changes in its mental health-related scales.