NORMALIZATION OF SPINE DENSITOMETRY

We investigated several transformations of bone mineral content (BMC) and area density (BMD), in particular volumetric density (BMAD), to as certain the influence on (1) body size dependence, (2) diagnostic sens itivity, and (3) precision. These transformations were examined in a g roup of 657 normal postmenopausal women and 327 women with osteoporoti c fracture. First, expression of results as BMAD removed some of the s light dependence on body size; 21% of the variation in BMC and 15% of the variation in BMD were associated with body weight, but only 8% wit h BMAD. Second, the Z scores compared with those for age-matched contr ols for BMD and BMC were -1.85 and -1.71, respectively; the Z score fo r BMAD was -1.64. Third, the precision error for BMC was reduced by ex pressing results as BMD (1.1 versus 0.5%); BMAD degraded precision sli ghtly (0.7%). BMD appeared to be the optimal expression for bone densi tometry because it provided the best diagnostic sensitivity and lowest precision error; there was a minimal influence of body size on BMD re sults. This study also showed that osteoporotic women, even in the fir st postmenopausal decade, had low spine BMD, small vertebral area, and low body weight. Such women may be particularly at risk of crush frac ture.