Short-Term Urine Deoxypyridinoline Biological Variability in the First 5 Years after Menopause

There is evidence that bone turnover in women is more rapid during the first years after menopause than in subsequent years. The assessment of deoxypyridinoline (DPD) cross-links in a fasting urine sample is considered a specific index of bone resorption by osteoclasts and also can be used for monitoring the response to pharmacologic antiresorption treatment. The interpretation of results, however, is hampered by biological and other preanalytical variability (1)(2)(3)(4). Specific degradation products of the bone matrix, such as DPD and pyridinoline (PYD), closely reflect the rate of bone metabolism. Vesper et al. (1) reported mean within-day variabilities of 67% for DPD (range, 53%–75%) and 71% for PYD (57%–78%). The mean between-day variability was 16% for both PYD and DPD (ranges, 5%–24% and 12%–21% for DPD and PYD, respectively). The mean between-person variabilities across different studies were 34% for DPD (8%–98%) and 26% for PYD (12%–63%) in healthy premenopausal women and 40% (27%–54%) and 36% (22%–61%), respectively, in postmenopausal women. Specimen instability and errors in creatinine measurements were additional sources of variability(1). Some authors have reported that the variability can be reduced by collecting urine for 24 h (or longer) instead of using single voids and by expressing the results as ratios to creatinine(5)(6). The usefulness of urinary markers of bone turnover in monitoring therapy depends on the within-person variability of these markers compared with their changes in response to treatment (7). Thus, the biological and laboratory variabilities of DPD cross-links are important considerations for clinical evaluation. We evaluated the biological variability of DPD cross-link concentrations in fasting morning urine specimens collected during a 2-week period from women in their first years of menopause. We examined 64 postmenopausal women (mean age, 53 years; range, 49–57 …