Clinical usefulness of measurements of urinary deoxypyridinoline (DPD) in patients with postmenopausal osteoporosis receiving intermittent cyclical etidronate: advantage of free form of DPD over total DPD in predicting treatment efficacy

Deoxypyridinoline (DPD) in urine, which reflects systemic bone resorption, is considered useful for assessing the effects of osteoporosis treatment. However, there are various methods of measuring DPD in urine but have been few comparative studies of the effectiveness of these methods. In this study, we investigated 94 postmenopausal women (63 patients administered with intermittent cyclical etidronate (ICE), and 31 control patients) focusing on total DPD and free DPD, measured by high-performance liquid chromatography (HPLC) and enzyme-linked immunosorbent assay (ELISA), respectively. For other metabolic bone markers, i.e., tartrate-resistant acid phosphatase (TRAP), bone-specific alkaline phosphatase (BAP), and osteocalcin (OC), we also investigated the ability of these markers to predict increases in bone mineral density (BMD), by employing receiver operating characteristic (ROC) analysis in relation to increasing BMD following ICE therapy, and we determined the usefulness of the different metabolic bone markers, using the signal-noise ratio derived from the mean significant change (MSC), which is double the day-to-day coefficient of variation in healthy volunteers. In the same way, we defined a significant change in BMD as double the mean change in BMD for 6 months after the initiation of observation in the control group, and we used this value as the cutoff value for ROC analysis. It was found that the assessment of urinary DPD was useful for assessing the treatment efficacy of ICE, and the assessment of changes at week 12 of therapy was most effective. In order to recognize changes in metabolic bone markers when the MSC is considered as the cutoff value, it is useful to assess the change in total DPD by HPLC. However, in order to predict increases in BMD 6 months or more after the initiation of ICE, it seems more effective to measure free DPD by ELISA. We conclude, therefore, that the measurement of free DPD by ELISA is more useful, especially when treatment efficacy of ICE is clinically predicted in individual patients with osteoporosis.