A comparison of reference bone mineral density measurements derived from two sources: referred and population based.

The construction of reference ranges for bone mineral density (BMD) is of importance when defining risk of osteoporosis in an individual. This study examined lumbar spine BMD from two different populations of women aged 40-69 years, both measured by dual X-ray absorptiometry (DXA) using Hologic QDR-1000 machines. Results were compared with the manufacturer's reference range. At one site (Centre 1) women were referred by general practitioners for BMD measurement to aid decisions regarding long term hormone replacement therapy (HRT). At the other (Centre 2), women were drawn from the age/sex register of a London general practice (population 11,000) and invited to attend a screening examination at their local hospital. The BMD for both groups did not differ significantly from the manufacturer's reference range. The BMD at Centre 1 was lower than Centre 2 by 0.0175 g cm-2 but this did not reach significance and after calibration of both DXA machines with a spine phantom the difference in BMD of the two groups was reduced to only 0.0034 g cm-2. Population based sampling carries no advantage over a GP referral based method for the construction of spinal BMD reference ranges. Although local BMD reference ranges may be required for sites outside the spine the comparable results in this study of the two UK reference ranges and those of the USA manufacturer suggest that local reference ranges for lumbar spine BMD using DXA may be unnecessary in the UK.