Objective evaluation of physical functioning after tumor necrosis factor inhibitory therapy in patients with ankylosing spondylitis: a selection of 3 feasible performance-based tests.

Objective: (1) To select a limited number of performance-based tests that are reliable, show improvement in physical functioning after tumor necrosis factor inhibitor (TNFi) therapy in patients with ankylosing spondylitis (AS), and generate information equivalent to the full set of tests, and (2) are feasible for use in daily clinical practice.

Methods: Eight performance-based tests were evaluated. To eliminate redundant testing, the tests that showed adequate reliability, the highest standardized response mean (SRM), and the largest proportion of patients with an improved performance-based physical functioning were selected. The selected tests were combined into a new criterion for improvement in physical functioning (AS Performance-based Improvement; ASPI). The number and percentage of improved patients identified with the ASPI and identified with the full set of performance tests were compared.

Results: Reliability for all tests was adequate to excellent (ICC 0.73-0.96). The tests for bending, putting on socks, and getting up from the floor had the highest SRM (0.52-0.74) and showed the largest proportion of improved patients after TNFi therapy. The combination of these 3 tests was feasible in daily clinical practice and showed improved physical functioning after TNFi therapy in 67% of the patients.

Conclusion: The 3 selected tests are recommended for use in daily practice because they generate information comparable to the full set. They are reliable and feasible, and the combination of these tests showed improved physical functioning after TNFi therapy in 67% of the patients. Evaluation of physical functioning might be improved by adding these tests to other AS outcome measures.