Cut-off values of distal forearm bone density for the diagnosis of central osteoporosis in black postmenopausal South African women

Abstract

Background: The objective of this study was to establish a triage cut-off point or threshold for peripheral bone mineral density (BMD), applicable to black postmenopausal women, and that could be used as a screening method to differentiate between women with normal BMD, and those with possible central osteoporosis. This was a cross-sectional study design conducted in the North West province. Central and peripheral BMD was measured in 184 black, urban postmenopausal women. Method: Receiver operating curves (ROC) analysis was used to establish cut-off points. Sensitivity, specificity, positive and negative predictive value, odds ratios and likelihood ratios were determined. Results: The results showed a prevalence rate of 41.3% for central osteoporosis. The area under the curve (AUC) for osteoporosis at the hip was 0.818, and for the spine, it was 0.771. Using the optimum cut-off point (0.371 g/cm2 ), our results showed a misclassification rate of ≈ 49% for spine osteoporosis, and a negative predictive value of 0.825. Women who had a forearm BMD below this threshold were ~10 times more likely to have osteoporosis of the spine. Conclusion: We recommend using 0.371 g/cm2 as a cut-off point to differentiate between women who have normal BMD, and those with possible osteoporosis of the spine.