Inappropriate reference range for peak bone mineral density in dual-energy X-ray absorptiometry:: Implications for the interpretation of T-scores

An inappropriate reference range for peak bone mineral density (BMD) may result in identification of an incorrect proportion of subjects with osteopenia and osteoporosis at dual-energy X-ray absorptiometry (DXA). In this study, we assessed the prevalence of low BMD in Turkish young adults with respect to local population reference range T-scores and the US reference range T-scores. The BMD values of lumbar spine (L1-L4) and proximal femur (femoral neck, intertrochanter, trochanter, Ward's triangle and total) were measured by DXA in 323 healthy young adults (171 women, 152 men) aged 19-25 years. The World Health Organization criteria for the diagnosis of osteopenia (-2.5 <T-score <-1) and osteoporosis (T-score less than or equal to -2.5) were applied. In women, the means of the US reference range T-scores were significantly lower than zero at the spine and proximal femoral sites (p<0.0001). In men, the means of the US reference range T-scores were significantly lower than zero at the spine, femoral neck, intertrochanter, total femur (p<0.0001) and trochanter (p<0.05), but not at Ward's triangle (p=0.92). When the diagnoses were based on local population reference range T-scores instead of the US reference range T-scores, the prevalence of low BMD (T-score <-1) in women fell from 50.3% to 14.0% at the lumbar spine and from 60.8% to 14.6% at the femoral neck, and in men from 42.8% to 15.8% at the lumbar spine and from 30.9% to 17.1% at the femoral neck. Our data suggest that individual populations should use their own reference range T-scores to avoid misdiagnoses of osteopenia and osteoporosis by DXA.