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Garrett S, Jenkinson T, Kennedy LG, Whitelock H, Gaisford P, Calin A. A new approach to defining disease status in ankylosing spondylitis: the Bath Ankylosing Spondylitis Disease Activity Index. J Rheumatol 1994;21(12):2286–91.

Reproducibility of the Bath Ankylosing Spondylitis Indices of disease activity (BASDAI), functional status (BASFI) and overall well-being (BAS-G) in anti-tumour necrosis factor-treated spondyloarthropathy patients.

Establishment of the minimum clinically important difference for the bath ankylosing spondylitis indices.

Evaluation of the smallest detectable difference in outcome or process variables in ankylosing spondylitis.

A new approach to defining disease status in ankylosing spondylitis: the Bath Ankylosing Spondylitis Disease Activity Index (English).

Portuguese version of the Bath indices for ankylosing spondylitis patients: a cross-cultural adaptation and validation.

Evaluation of a French version of the Bath Ankylosing Spondylitis Disease Activity Index in patients with spondyloarthropathy.

The BASDAI questionnaire using VAS is available in the original publication. Available online (in multiple translations) at http://www.asas-group.org and at http://www.asif.rheumanet.org/.

Patient self-administered questionnaire used to measure patient-reported disease activity in patients with AS/axial SpA. The instrument was first published in 1994 using visual analogue scales. The use of numerical rating scales has also been validated. The index includes patient-reported levels of back pain, fatigue, peripheral joint pain and swelling, localized tenderness, and the duration and severity of morning stiffness.

The scores for questions 5 and 6 (severity and duration of morning stiffness) are averaged; the result is then averaged with the remaining 4 question scores to give a final score out of 10.

α = 0.84-0.87

ICC = 0.94 (0.91–0.95)

SDD = 1.96

95% CI of 95% limits of agreement = -2.32 to 2.23

Developed by experts in the field with patient input (however the role of patients is not made explicit).

Evidence using principal component analysis supports structural validity of the single domains of the BASDAI.

BASDAI correlated well with the earlier Bath Disease Activity Index with no significant differences in score distribution, reproducibility, or sensitivity.

Good correlation with the Ankylosing Spondylitis Quality of Life questionnaire (Pearson’s correlation coefficient = 0.79) and BASDAI was significantly higher in AS patients unable to work due to AS.

Moderate correlation with BASFI (Spearman´s correlation coefficient = 0.45), SF36-PCS (Spearman´s correlation coefficient = -0.47) and weak correlation with SF36-MCS (Spearman´s correlation coefficient = -0.25).

BASDAI has been translated, adapted and validated in several languages and countries.

The modified standardized response mean measured against AS health transition is reported as -0.74 for improvement and 0.60 for deterioration in health (p<0.01), and measured against general health transition is -1.02 for improvement and 0.74 for deterioration.

Initial evaluation of the patient acceptable symptom state (PASS) in AS patients (Dougados et al) found the mean change in BASDAI over 12 weeks for the patient to feel well was -3.5 (SD 2.3), and there was significant correlation between the BASDAI 50% responders and patients achieving PASS. A PASS cut off of 3.45 cm (95% CI 3.09–3.89 cm) has been described.

Distribution of scores across the scale has been shown to be good (score range: 0.5-10; mean: 4.31 in the first description). There have been no floor or ceiling effects reported.

MCID = 1 cm or 22.5% (with SE=65% and SP=82%, on ROC curve analysis using patient report of important change as the gold-standard).

Another study indicated that the smallest detectable difference was 1.96 (in a 0-10 scale), based on Bland-Altman´s technique.

A comparison of the Bath Ankylosing Spondylitis Disease Activity Index and a modified version of the index (mini-BASDAI) in assessing disease activity in patients with ankylosing spondylitis without peripheral manifestations was published in 2009 by Song et al (http://www.ncbi.nlm.nih.gov/pubmed/19029168).

Mini-BASDAI excludes the questions about peripheral arthritis (question 3) and enthesitis (question 4).

The authors assessed the correlation of the original BASDAI and the mini-BASDAI with patient global and other disease parameters was assessed in a total of 692 patients from three AS cohorts including one observational AS cohort and two clinical trial populations treated with non-steroidal anti-inflammatory drugs and tumour necrosis factor alpha inhibitors. Sensitivity to change was also assessed by calculating effect sizes.

The mini-BASDAI had higher values compared with the original BASDAI, also in the subgroup with peripheral manifestations. However, the mini-BASDAI did not correlate better with other markers of disease activity compared with the original BASDAI. Furthermore, effect sizes of the original BASDAI and mini-BASDAI were comparable in the treatment trials. Approximately 5% of active AS patients with pure axial disease manifestation were identified whose disease activity was underestimated by the original BASDAI.

The authors concluded that on a group level using the mini-BASDAI did not result in an advantage to assess disease activity or in the subgroup without peripheral involvement. In only approximately 5% of AS patients was the mini-BASDAI superior to the original BASDAI.