Bath Ankylosing Spondylitis Disease Activity Index (Garrett 1994).

What it is and when to use it

The BASDAI (Bath Ankylosing Spondylitis Disease Activity Index) is a patient-reported questionnaire that measures disease activity in axial spondyloarthritis, including ankylosing spondylitis. It assesses six domains using 0-10 numerical scales: fatigue, axial pain (neck, back, hips), pain and swelling in peripheral joints, tenderness to pressure (enthesitis), and the duration and severity of morning stiffness. It is used in clinical practice and trials to monitor symptomatic activity and was one of the reference tools recommended by ASAS (Assessment of SpondyloArthritis international Society) and EULAR, now complemented by the ASDAS.

How to interpret it

The final score ranges from 0 to 10, with higher scores indicating greater disease activity. The most established threshold is BASDAI ≥ 4, which reflects active disease and has often been used as a criterion to consider or evaluate response to biologic therapy. Values below 4 suggest low or controlled activity. BASDAI is best interpreted longitudinally: a meaningful reduction from baseline (for example, an improvement of ≥ 2 points) indicates a treatment response.

Limitations and when not to use it

BASDAI is validated in adults with axial spondyloarthritis and ankylosing spondylitis; it is a subjective measure based solely on the patient's perception. It does not assess objective inflammatory activity (it includes no CRP/ESR or imaging) nor structural damage or spinal mobility, for which the BASFI or BASMI are needed. A common misuse is relying on it in isolation to make treatment decisions: guidelines recommend combining it with objective parameters, and the ASDAS (which incorporates CRP) provides a more complete assessment of activity.

Frequently asked questions

What BASDAI score indicates active disease?

A score of 4 or higher (on the 0-10 scale) is considered indicative of active disease and has commonly been used as a threshold to evaluate initiation of biologic therapy.

What is the difference between BASDAI and ASDAS?

BASDAI relies only on patient-reported symptoms, whereas the ASDAS combines patient items with an acute-phase reactant (CRP or ESR), making it a more objective measure of disease activity.

How is the BASDAI score calculated?

The two morning-stiffness questions are averaged and that value is added to the other four responses; the total is divided by 5 to yield a final score from 0 to 10.