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Objectives: The current World Health Organization (WHO) definition of osteoporosis, which is based on densitometry of lumbar and femoral regions, is extensively used for decision-making in clinical practice. Discordance in diagnosis of osteoporosis using this definition is a known phenomenon. The aim of this study was to evaluate the impact of such discordance and to assess the diagnostic value of using one skeletal site for screening purposes as opposed to the two sites required in the WHO criteria. Study design: Data was collected from 4188 individuals (3848 female); mean age = 53.4 years (standard deviation 11.8) referred to a community-based outpatient osteoporosis testing centre in Tehran, Iran. Methods: Dual-energy X-ray absorptiometry (DXA) was performed on L1-L4 lumbar spine and total hip for at[ cases. The DXA results were categorized according to WHO criteria. Sensitivity for each site was calculated as number of cases with T-score <-2.5 at that site divided by the total number of cases with T-score <-2.5 at any site. Results: Prevalence of osteoporosis diagnosis using lumbar DXA, femoral DXA, and WHO criteria (either of the sites) were 24.7%, 12.4%, and 27.8%, respectively. Sensitivity of lumbar DXA for diagnosis of osteoporosis (88.9%) was significantly higher than femoral DXA (44.6%, P<0.001); but this difference became non significant for men >-60 and women >-70 (P = 0.615 and P = 0.077, respectively). Agreement of the procedures in different sites (κ) was 0.40 (0.37 to 0.43). When proximal femur was considered as the reference, positive likelihood ratios of lumbar DXA to detect cases were 4.7 and 2.0 in younger and older groups, respectively. Conclusions: Concerning the high rate of discordance and low agreement between DXA results, the data obtained from each anatomical site cannot predict the condition of the other site. However, if use of a single assessment is intended for screening programs, public health authorities can develop... [ABSTRACT FROM AUTHOR]