BMD reference standards among South Asians in the United States

The relationship between bone mineral density (BMD) and fracture risk is not well established for non-white populations. There is no established BMD reference standard for South Asians. Dual-energy X-ray absorptiometry (DXA) was used to measure BMD at total hip and lumbar spine in 150 US-based South-Asian Indians. For each subject, T-scores were calculated using BMD reference values based on US white, North Indian, and South Indian populations, and the resulting WHO BMD category assignments were compared. Reference standards derived from Indian populations classified a larger proportion of US-based Indians as normal than did US white-based standards. The percentage of individuals reclassified when changing between reference standards varied by skeletal site and reference population origin, ranging from 13% (95% confidence interval [CI]: 7-18%), when switching from US white- to North Indian-based standard for total hip, to 40% (95% CI: 32-48%), when switching from US white to South Indian reference values for lumbar spine. These findings illustrate that choice of reference standard has a significant effect on the diagnosis of osteoporosis in South Asians, and underscore the importance of future research to quantify the relationship between BMD and fracture risk in this population.