Stability of the Patient Acceptable Symptomatic State over time in outcome criteria in ankylosing spondylitis

Objective. The Patient Acceptable Symptomatic State (PASS) is the highest level of symptoms beyond which patients consider themselves well. It provides clinically meaningful information to interpret results from scales or questionnaires. Our goal was to determine the PASS in main outcome criteria when assessing patients with ankylosing spondylitis (AS) and to evaluate whether the PASS is stable over time. Methods. We used data from a randomized controlled trial of 330 patients with AS. The PASS was estimated at weeks 2, 6, and 12 for the following patient-reported outcomes: global pain (measured on a visual analog scale [VAS]), nocturnal pain (VAS), patient's global assessment of disease activity (VAS), disease activity (Bath Ankylosing Spondylitis Disease Activity Index [BASDAI]), and functional impairment (Bath Ankylosing Spondylitis Functional Index [BASFI]). We used an anchoring method based on patients answering yes or no to, "Is your current condition satisfactory, when you take your general functioning and your current pain into consideration?" The PASS was defined as the 75th percentile of the score for patients who considered their state satisfactory. All patients were considered together in the analysis. Results. The values (95% confidence interval) of PASS were 33.5 (29.2-38.6) for pain, 28.0 (23.1-34.1) for night pain, 35.7 (31.3-41.1) for patient's global disease assessment, 31.4 (26.9-37.0) for BASFI, and 34.5 (30.9-38.9) for BASDAI. The PASS estimates were stable over time for all criteria during followup. Conclusion. This study provides cutoff values for the PASS for the main outcome measures in AS and shows that PASS values are stable over time.