In evaluating techniques for measuring BMD, the critical parameters are the accuracy and precision of the instrument. Compared with the hip or spine, soft tissue attenuation is less of a concern in measuring BMD of the heel and wrist, which are embedded in thinner, and more consistent, layers of soft tissue.
Precision relates to the reproducibility of the technique.
Precision is most critical when serial measurements of BMD are performed to assess response to therapy. The slow rate of bone loss, and the lack of exquisite precision in the technologies, means that, in some cases, significant changes in BMD can only be reliably measured over an interval of several years. This limitation of serial measurements has spurred interest in measuring serum and urine markers of bone turnover.