ORIGINAL ARTICLE Burcu Yanık Æ Yes ¸ im Kurtais ¸ Gu¨rsel Æ S ¸ ehim Kutlay Saime Ay Æ Atilla Halil Elhan Adaptation of the Bath Ankylosing Spondylitis Functional Index to the Turkish population, its reliability and validity: functional assessment in AS Received: 10 November 2003 / Accepted: 7 May 2004 / Published online: 8 September 2004 Ó Clinical Rheumatology 2004 Abstract The aim of this study was to adapt the Bath Ankylosing Spondylitis Functional Index (BASFI) to the Turkish population and investigate the reliability and the validity of the Turkish version. Seventy-six patients with ankylosing spondylitis (AS) were included in the study. The functional status of the patients was assessed by using the adapted Turkish version of the BASFI twice, at recruitment and 24 h later. For validity analysis, patients were also assessed by the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) evaluating disease activity, the Bath Anky- losing Spondylitis Global Score (BAS-G) indicating effect of the disease on patient’s well-being, physician’s assessment of the disease activity and pain intensity. Spinal mobility was assessed by the Bath Ankylosing Spondylitis Metrology Index (BASMI). Erythrocyte sedimentation rate (ESR) and serum C-reactive protein (CRP) levels of the patients were also recorded. The lumbar region and the sacroiliac joints were assessed by Stoke Ankylosing Spondylitis Spine Score (SASSS) and the hip joints were assessed by Bath Ankylosing Spondylitis Radiology Index hip (BASRI-h). The internal consistency was 0.89 (Cronbach’s alpha), which showed a high reliability for the Turkish version of the BASFI. Test-retest reliability was good, with a high intraclass correlation coefficient between the two time points (ICC=0.93). Significant correlations were detected between the BASFI and the BASDAI, BAS- G, doctor’s global assessment, and general pain inten- sity (r=0.62, p<0.001; r=0.47, p<0.001; r=0.55, p<0.001; r=0.47, p<0.001, respectively). The adapta- tion of the BASFI to the Turkish population was successful and it was found to be reliable and valid among Turkish patients. Thus, studies using the Turkish BASFI can be compared with international studies. Keywords Adaptation Æ Ankylosing spondylitis Æ Functional index Æ Reliability Æ Validity Introduction Ankylosing spondylitis (AS) is a chronic and progres- sive disease and unfortunately there are no definite measures to evaluate the outcome. Changes in clinical, laboratory, and radiological findings between visits do not in general correlate with the improvements or deteriorations [1, 2, 3]. Clinical findings may yield some information, but a consensus on what type of mea- surements should be used and how much they reflect the patient’s status is not established. Laboratory findings are proven to be uncorrelated with the status of the patient. Radiological findings are important in terms of the long-term outcome, but are not correlated with rapid disease progress. Even if frequent X-rays were useful in evaluating the progress of the disease, the excessive cost and potential health hazards outweigh the benefits [1]. The lack of clear-cut measures in evaluating the status of the patient makes it difficult to assess the effectiveness of all treatment modalities. To tackle this problem, the Assessment in Ankylosing Spondylitis (ASAS) [4] group, a group of experts dealing with AS, has recommended a core set to be used in clinical trials involving patients with AS. Here, the level of functional impairment has been proposed to B. Yanık Æ Y. K. Gu¨rsel Æ S¸. Kutlay Æ S. Ay Department of Physical Medicine and Rehabilitation, School of Medicine, Ankara University, Ankara, Turkey B. Yanık(&) 23. Cadde Simkent Sitesi, 3. Blok, No: 8/14 Kırkkonaklar, C¸ ankaya, Ankara, Turkey E-mail: burcucorek@hotmail.com Tel.: +90-532-5833545 Fax: +90-312-3094132 A. H. Elhan Department of Biostatistics, School of Medicine, Ankara University, Ankara, Turkey Clin Rheumatol (2005) 24: 41–47 DOI 10.1007/s10067-004-0968-6