The Minimum Clinically Important Improvement and Patient-acceptable Symptom State in the BASDAI and BASFI for Patients with Ankylosing Spondylitis.

Objective: To establish cutoffs for the minimum clinically important improvement (MCII) and the patient-acceptable symptom state (PASS) for the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) and the Bath Ankylosing Spondylitis Functional Index (BASFI) in patients with ankylosing spondylitis (AS).

Methods: Patients with AS who started nonsteroidal antiinflammatory drugs were included. After 4 weeks, the PASS and the MCII were defined using external anchor questions (for the PASS, patients considering their condition of AS over the prior 48 h as "acceptable" forever; and for the MCII, those reporting moderate or slightly important improvement).