Purpose: To assess the ability of the urinary N-telopeptide of type I collagen (NTx) to monitor and predict therapeutic effects of hormone replacement therapy (HRT) in postmenopausal women.
Patients and methods: To assess the relationship between baseline or change in NTx (predictive variable), and change in lumbar and hip bone mineral density (BMD; outcome variable), we conducted a 2-year randomized controlled study at academic university and private practice medical centers in 236 healthy women 1 to 3 years postmenopausal; 227 women completed the study. Women received estrogen plus progesterone plus calcium (treated group) or calcium alone (control group).
Results: In the treated group NTx significantly (P < 0.0001) decreased, and spine and hip BMD significantly (P < 0.00001 and P < 0.005, respectively) increased; in the control group NTx did not change but BMD decreased significantly (P < 0.01). Subjects in the highest quartiles for baseline NTx (67 to 188 units) or decreasing NTx (-66% to -87%) through 6 months demonstrated the greatest gain in BMD in response to HRT (P < 0.05 and P < 0.005). For every increase of 30 units in baseline NTx the odds of gain in BMD in response to HRT increased by a factor of 5.0 (95% confidence interval [CI] 1.9 to 13.3); for every 30% decrease in NTx through 6 months, the odds of gaining BMD in response to HRT increased by a factor of 2.6 (95% CI 1.6 to 4.4). In the control group an increase of 30 units in mean NTx across the study indicated a higher odds of losing BMD by a factor of 3.2 (95% CI 1.6 to 6.5). A high baseline NTx (> 67 units) indicated a 17.3 times higher risk of BMD loss if not treated with HRT.
Conclusion: These data support the clinical utility of NTx to monitor the antiresorptive effect of HRT in recently postmenopausal women, and to predict changes in BMD in response to HRT.