Osteoporosis related fractures are common in old age and over 40 % of the women above 50 years of age are at a risk of developing a fragility fracture. Biochemical markers of bone turnover (BTMs) have proven to be of some value in fracture predictability. There is also a correlation between rate of decrease of areal bone mineral density (aBMD) and incident fractures.
In this series of studies, the correlation between BTMs and rate of bone loss (change of aBMD and ultrasound variables) over 5 years was investigated in a cohort of 75 year-old Swedish women. In addition, correlation of BTMs and bone metabolism, as assessed by scintigraphy, was tested in postmenopausal women. Finally, the effect of precision error on the longitudinal monitoring of change in aBMD was assessed in elderly women and in elderly men.
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 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 aBMD change beyond the least significant level in more than 50% of elderly individuals ranged from 332 years, and was dependent on the equipment used and the skeletal site tested.
These results indicate that BTMs are associated with future bone loss although the correlations may not be strong enough to predict bone loss at individual level. DXA also has some limitations when used in longitudinal follow up of elderly individuals. DXA is therefore of limited use in the longitudinal monitoring ofbone loss. Further studies with novel bone turnover markers may improve the ability of BTMs to predict bone loss.