THE BATH ANKYLOSING-SPONDYLITIS PATIENT GLOBAL SCORE (BAS-G)

In the absence of an ideal objective measure for assessing ankylosing spondylitis (AS), self-administered measures of disease activity (the Bath Ankylosing Spondylitis Disease Activity Index, BASDAI) and functi on (the Bath Ankylosing Spondylitis Functional Index, BASFI) have been developed, in addition to an objective measure of spinal mobility (th e Bath Ankylosing Spondylitis Metrology Index, BASMI). However, a more global assessment is also desirable. We report on the design and vali dation of a global measure (the Bath Ankylosing Spondylitis Patient Gl obal Score, BAS-G) which reflects the effect of AS on the patient's we ll-being. A pilot study was performed to select the most appropriate w ording for BAS-G. Using 392 patients with AS, BAS-G's construct and pr edictive validity and test-retest reliability were assessed. Correlati ons between BAS-G and BASDAI/BASFI were calculated, and multiple regre ssion was used to examine the significant correlates. The distribution of the responses covered the whole scale. As predicted, BAS-G correla ted best with BASDAI (r = 0.73), followed by BASFI (r = 0.54). The bes t fitting regression equation included these scales as well as patient s' gender and current age. One week and 6 month scores were significan tly different (P < 0.001). Construct validity was good: BAS-G correlat ed more strongly with each component of BASDAI and BASFI than with BAS MI or with gender. Predictive validity was satisfactory: there was an improvement (mean = 29%) in in-patient BAS-G scores over a 2 week trea tment period (P < 0.001). Test-retest reliability was excellent (1 wee k r = 0.84, 6 months r = 0.93). BAS-G correlates well with both BASDAI and BASFI, suggesting that disease activity and functional ability pl ay a major role in patients' well-being, whereas metrology does not. T he score is sensitive to change, reliable, and meets face, predictive and construct validity criteria.