Diagnostic utility of serum TRACP5b for secondary osteoporosis in ankylosing spondylitis: a comparative cross-sectional study with primary osteoporosis and healthy controls

Serum TRACP5b may serve as a supplementary marker of osteoclast activity in AS and shows moderate diagnostic value for secondary osteoporosis, with levels more related to age and disease activity than BMD. Larger studies are needed to confirm its clinical utility. Key Points • Serum TRACP5b levels were higher in patients with AS than in healthy controls, though without consistent statistical significance, reflecting biological variability. • TRACP5b correlated positively with age and disease activity (BASDAI) in AS but not with BMD, disease duration, or ESR, highlighting its link to inflammatory bone resorption. • ROC analysis showed TRACP5b had moderate diagnostic performance for secondary osteoporosis in AS, but limited value in primary osteoporosis. • Our findings suggest that TRACP5b may serve as supplementary marker of bone turnover in AS, warranting further validation in larger, longitudinal studies.