Bone mineral density discordance and exploration of one of its causes

Discordances between hip and spine areal density T-score values are common and incompletely understood. In a cohort of 1157 postmenopausal women, discordances of greater than 10% occurred in 91%, with spine bone mineral density (BMD) T-scores significantly less negative than femoral neck (FN) T-scores (p<0.001). However, when T-scores based on bone mineral content (BMC) rather than BMD were used, the mean discordance was not significantly different from 0. This was largely because BMC at the FN had seemingly declined with age less rapidly than had BMD at that site. This can be explained by age-related areal expansion at the hip, which would be missed in the reported BMD output. One consequence is that if BMC-based T-scores are used to classify patients, substantially fewer individuals would have been judged osteoporotic in this cohort (two-thirds fewer for spine and three-fourths fewer for hip).