REFERENCE GENTILE CHARTS FOR MEASURES OF DISEASE-ACTIVITY, FUNCTIONALIMPAIRMENT, AND METROLOGY IN ANKYLOSING-SPONDYLITIS

Objective. To construct reference centile charts for validated measure s of disease activity, functional impairment, and metrology (the Bath Ankylosing Spondylitis Disease Activity Index [BASDAI], Bath Ankylosin g Spondylitis Functional Index [BASFI], and Bath Ankylosing Spondyliti s Metrology Index [BASMI]) in a population of patients with AS, and to explore the potential application of these charts in patient care and clinical research. Methods. We collected BASDAI and BASFI data on 2,9 79 patients with AS from the Royal National Hospital for Rheumatic Dis eases (RNHRD) database and BASMI data on 393 patients at RNHRD. Data o n age, sex, and duration of AS were also obtained. Gentile charts were constructed for the BASDAI, BASFI, and BASMI in both males and female s, with duration of AS as the time-dependant variable. Where necessary , BASDAI, BASFI, and BASMI ram scores were transformed to ensure that the indices were normally distributed over the range of disease durati on, and allowance was made for change in variability of the indices. R esults. Linear models were fitted to the mean and standard deviations of BASDAI, BASFI, and BASMI scores in males and females as a function of disease duration. A standard deviation score plot confirmed goodnes s of fit of the models, and fitted centiles were derived. Charts showi ng the 5th, 10th, 25th, 50th, 75th, 90th, and 95th centiles were const ructed. The charts confirmed that AS remains active after 40 years' du ration (mean BASDAI score 2.22 and 2.99 in males and females, respecti vely). The charts also demonstrated that females have greater disease activity and more functional impairment than males, despite better met rology. Conclusion. The use of centile reference charts for disease ac tivity, functional impairment, and metrology in AS will allow physicia ns and patients to interpret index scores relative to a reference popu lation and will provide the opportunity to assess change over time and response to therapeutic interventions, to improve definition of disea se status, and to enhance patients' involvement in their care.