DIAGNOSIS OF OSTEOPOROSIS BY PLANAR BONE DENSITOMETRY - CAN BODY-SIZEBE DISREGARDED

Bone densitometry using dual energy X-ray absorptiometry (DXA) is freq uently used to diagnose osteoporosis and to identify patients at risk of later fractures. The parameters of interest are bone mineral conten t (BMC) and bone mineral areal density (BMD). Bone densitometry result s have a large overlap between normals and patients with fractures. Th is would suggest that other factors are important for the development of fractures or that bone densitometry is not used optimally. It is ge nerally believed that the conversion of BMC to BMD by division of the former by the projected bone area is a good normalization procedure. O ther normalization procedures have been attempted in the past with lit tle success. We hypothesized that this might be due to a blurring effe ct of time since menopause, and that body size could be demonstrated t o have an effect on measured BMC and BMD, if this time effect could be eliminated. The results of this study, comprising 1625 early post-men opausal women studied at virtually the same time since menopause, conf irm that this is the case. Body surface area was the parameter among c onventional body size variables showing the highest correlation with B MC and BMD. It was clearly shown that low values of BMD were seen more often in the lowest than in the highest body surface area quartile. T he difference between quartiles was statistically significant. Simple division of BMC by actual body surface area or division of BMD by the square root of body surface removed the uneven distribution between th e body surface area quartiles for lumbar spine and femoral neck measur ements, and reduced it at peripheral measuring sites. It is suggested that BMC and BMD of the lumbar spine and the femoral neck should be no rmalized as described to avoid overdiagnosis of osteoporosis in person s of petite body stature and underdiagnosis in tall ones.