Serum cathepsin K levels are not suitable to differentiate women with chronic bone disorders such as osteopenia and osteoporosis from healthy pre- and postmenopausal women.

Objectives: Cathepsin K (CatK) is expressed in high levels in osteoplasts and therefore plays an important role in bone resorption. Thus CatK serum levels may be useful in the diagnosis of chronic bone disorders such as osteopenia and osteoporosis. Therefore we aimed at studying CatK levels in women putatively free of known skeletal disorders.
Study Design: In total, 121 voluntary women, 27 premenopausal women aged between 20 and 45 years, and 94 postmenopausal women aged 59-81 years, all free of known skeletal disorders were included. All women underwent bone density measurement, routine labor parameter and measurement of serum CatK levels.
Main Outcome Measures: Based on WHO criteria, women were stratified in four groups (premenopausal: healthy; postmenopausal: healthy, osteopenia, osteoporosis), and their CatK levels were statistically analyzed.
Results: Using WHO criteria 21 postmenopausal women had normal bone mineral density (BMD), 49 had osteopenia and 24 had osteoporosis. All 27 premenopausal women had normal BMD. There were no significant differences in CatK between these groups. ROC analysis resulted in poor diagnostic validity of CatK, where the area under curve was 0.544. There was no correlation neither between CatK and other biomarkers as C-telopeptide crosslaps (CTX) or bone-specific alkaline phosphatase (BAP) nor between CatK and age.
Conclusions: Serum levels of CatK are not suitable to differentiate women with osteoporosis from healthy subjects.
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