Diagnosis of osteoporosis by planar bone densitometry: can body size be disregarded?

Abstract

Bone densitometry using dual energy X-ray absorptiometry (DXA) is frequently used to diagnose osteoporosis and to identify patients at risk of later fractures. The parameters of interest are bone mineral content (BMC) and bone mineral areal density (BMD). Bone densitometry results have a large overlap between normals and patient with fractures. This would suggest that other factors are important for the development of fractures or that bone densitometry is not used optimally. It is generally believed that the conversion of BMC to BMD by division of the former by the projected bone area is a good normalization procedure. Other normalization procedures have been attempted in the past with little success. We hypothesized that this might be due to a blurring effect of time since menopause, and that body size could be demonstrated to have an effect on measured BMC and BMD, if this time effect could be eliminated. The results of this study, comprising 1625 early post-menopausal women studied at virtually the same time since menopause, confirm that this is the case. Body surface area was the parameter among conventional body size variables showing the highest correlation with BMC 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. The 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 the body surface area quartiles for lumbar spine and femoral neck measurements, and reduced it at peripheral measuring sites. It is suggested that BMC and BMD of the lumbar spine and the femoral neck should be normalized as described to avoid overdiagnosis of osteoporosis in persons of petite body stature and underdiagnosis in tall ones.

Efficacy of estrogen replacement therapy (ERT) on uterine growth and acquisition of bone mass in patients with Turner syndrome

“…Although it has been reported that the BMD of women with TS tends to be underestimated because of their short stature [25,26], it has been found that they have sufficient bone mass, similar to those in the MC group in which height is significantly lower. In addition, by using BMD of the MC group as a positive control, it was possible to compare the BMD of the amenorrhea group.…”

The Fallacy of BMD: A Critical Review of the Diagnostic Use of Dual X-ray Absorptiometry

“…In some countries a low Z-score (4-1.0) is the basis for reimbursement. Figure 1 exemplifies the significance of BSA correction of Z-scores for a large woman and a small one in case of lumbar spine BMD, using BSA quartiles and the data from [3]. It can be seen that if the BMD of the former (belonging to the highest quartile) were 0.900 g/cm 2 , she would have a Z-score of -1.31 and be entitled to reimbursement.…”

“…When BMC is converted to BMD by division with the projected bone area, a surrogate bone density is obtained. This parameter is also proportional with the bone size and body size, although less so than BMC [3]. In the following BMD will be the term for this two-dimensional variable only, whereas the threedimensional bone density of CT will be termed 3D-BMD.…”

“…Normalisation was performed by us in a large population of normal early postmenopausal women, lumbar spine BMC and hip BMC being divided by normalised BSA, and BMD of the same sites being divided by the square root of normalised BSA, with the result that the Z-scores became independent of body size and the overdiagnosis of petite women abolished [3]. Among 1625 early postmenopausal women divided into BSA quartiles, the number having a lumbar spine BMD Z-score (Hologic normal reference population) less than -1.0 was 102 for the lowest BSA quartile, in contrast to 25 women in the highest BSA quartile.…”

Normal Tempo of Bone Formation in Turner Syndrome despite Signs of Accelerated Bone Resorption

“…Many women with TS do not achieve normal peak bone mass [1,5,6]. Dual-energy X-ray absorptiometry (DXA) is commonly used in children and adults [7], but interpretation in TS is difficult due to an inherent tendency of DXA to underestimate area bone mineral density (aBMD) in short-statured patients [8]. Volumetric BMD (vBMD) has been found normal or near-normal in TS [9,10,11], but interpretations are challenging due to variations in pubertal status and height disparity during puberty [12].…”