Bath Ankylosing Spondylitis Disease Activity Index (BASDAI)

The Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) is a patient‑reported outcome measure designed to quantify disease activity in ankylosing spondylitis and axial spondyloarthritis. It uses six questions scored on numerical rating scales (0–10) covering fatigue, spinal pain, peripheral joint pain/swelling, localised tenderness (enthesitis) and the duration/severity of morning stiffness. These scores are combined to give a single BASDAI value from 0 (no activity) to 10 (very active disease).

Although originally developed for ankylosing spondylitis, BASDAI is widely used in people with axial involvement in psoriatic arthritis. It is simple, quick to complete and gives a more nuanced view of symptoms than a single global assessment. In trials and routine practice, thresholds such as BASDAI ≥ 4 or ≥ 6 are often used to define high disease activity and eligibility for biologic therapy, depending on national guidance and funding criteria.

There are some limitations: BASDAI is entirely symptom‑based and does not include inflammatory markers or imaging results. As such, it can be influenced by co‑existing conditions (for example, fibromyalgia) and may over‑estimate inflammatory activity in some patients. Composite indices like ASDAS (which incorporate C‑reactive protein or ESR) can complement BASDAI by incorporating objective measures of inflammation.

In everyday practice, BASDAI is useful for monitoring symptoms over time, evaluating response to treatment and supporting shared discussions around flare management, exercise and non‑pharmacological strategies.

• Key references
• Garrett S et al. A new approach to defining disease status in ankylosing spondylitis: the Bath Ankylosing Spondylitis Disease Activity Index. J Rheumatol. 1994;21(12):2286–2291.
• Braun J et al. Comparison of BASDAI and other outcome measures in axial spondyloarthritis. Ann Rheum Dis. 2002;61(Suppl 3):iii40–iii43.
• Urruticoechea‑Arana A et al. Psoriatic arthritis screening: a systematic literature review and experts’ recommendations. PLoS One. 2021;16(3):e0248571. (Discusses tools for axial and peripheral disease).

Reviewed: August 2026

Version ID: 2/BAS/AAR/08/26