Bone turnover markers and prediction of bone loss in elderly women
Abstract: Around 70,000 osteoporosis-related fractures occur in Sweden annually and approximately half of the women in western world will sustain a fragility fracture after the age of 50 years. Fracture preventive efforts require the identification of individuals who are at high risk. Biochemical markers of bone turnover (BTMs) have shown some degree of fracture predictability. There is also a correlation between rate of decrease of areal bone mineral density (aBMD) and incident fractures. In this study, the correlation between BTMs and rate of bone loss (change of aBMD and ultrasound variables) over 5 years was investigated in the Malmö OPRA cohort of 75-year old women (n = 506 to 601). In addition, correlation of BTMs and bone metabolism, as assessed by scintigraphy, was tested in postmenopausal women (n = 22). Finally, the effect of precision error on the longitudinal monitoring of change in aBMD was assessed in elderly women (n = 690) and in elderly men (n = 211). There was a strong correlation between all bone turnover markers and the results of scintigraphy (total skeletal uptake of 99mTc-labelled methylene diphosphonate), with no significant difference between bone formation markers and bone resorption markers. BTMs correlated to the 5-year rate of change of aBMD, especially in the legs and the total body, and 5-year change in speed of ultrasound. When serial measurements of BTMs were analysed, the mean value of measurements were correlated more strongly to aBMD change than single measurements, and women with constantly high levels of BTMs had higher rates of bone loss. Precision error of aBMD measurement by dual-energy X-ray absorptiometry has an influence on the detection of individuals with aBMD change exceeding the least significant level. The calculated follow-up interval for detection of a change in aBMD beyond the least significant level in more than half of the elderly individuals ranged from 3–32 years, and was dependent on the equipment used and the skeletal site tested. The results of this study indicate that currently available BTMs are associated with future bone loss. However, these correlations may not be strong enough to be predictive of bone loss at the individual level. DXA also has some limitations when used in the longitudinal setting in elderly individuals. DXA is therefore of limited use in the longitudinal monitoring of bone loss. Further studies with novel bone turnover markers may improve the ability of BTMs to predict bone loss.
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