Serum TRACP5b as a Diagnostic Marker for Secondary Osteoporosis in Ankylosing Spondylitis

Overview

This cross-sectional study evaluated serum TRACP5b levels in patients with ankylosing spondylitis (AS)-associated secondary osteoporosis compared to primary osteoporosis and healthy controls. Findings demonstrated that TRACP5b is elevated in AS patients with osteoporosis and correlates with disease activity and bone mineral density, supporting its potential as a diagnostic biomarker.

Background

Osteoporosis is characterized by reduced bone mineral density (BMD) and increased fracture risk, classified as primary or secondary based on etiology. Ankylosing spondylitis (AS) is an inflammatory rheumatic disease causing both new bone formation and bone loss, leading to secondary osteoporosis. Dual-energy X-ray absorptiometry (DXA) is the standard for BMD assessment but does not capture dynamic bone turnover changes. Tartrate-resistant acid phosphatase 5b (TRACP5b), a marker of osteoclast activity, may provide complementary information on bone resorption in AS.

Data Highlights

Key Findings

• Serum TRACP5b levels were significantly higher in AS patients with secondary osteoporosis compared to healthy controls.
• TRACP5b levels correlated positively with disease activity measured by BASDAI in AS patients.
• TRACP5b showed diagnostic utility in distinguishing secondary osteoporosis in AS from primary osteoporosis and healthy states, with favorable sensitivity and specificity.
• BMD was reduced in AS patients, consistent with secondary osteoporosis, despite the presence of new bone formation in AS pathology.
• TRACP5b measurement provides dynamic insight into osteoclast-mediated bone resorption not captured by DXA alone.

Clinical Implications

Serum TRACP5b may serve as a valuable biomarker to complement DXA in diagnosing and monitoring secondary osteoporosis in AS patients. Its correlation with disease activity suggests it could aid in assessing bone metabolic changes related to inflammation. Incorporating TRACP5b testing could improve fracture risk stratification and guide therapeutic decisions in this population.

Conclusion

Serum TRACP5b is a promising diagnostic marker reflecting osteoclast activity and bone resorption in ankylosing spondylitis-associated secondary osteoporosis. It enhances understanding of bone metabolism beyond static BMD measurements and may improve clinical management of osteoporosis in AS.

References

1. Modified New York criteria for AS diagnosis
2. WHO guidelines on osteoporosis diagnosis
3. Studies on TRACP5b as bone resorption marker