Unilateral vs bilateral hip bone mineral density measurement for the diagnosis of osteoporosis

It has not been established whether unilateral or bilateral hip dual-energy X-ray absorptiometry (DXA) is preferable for the diagnosis of osteoporosis. We investigated the discordance in DXA measurements in bilateral hips to determine whether unilateral DXA is valid for osteoporosis diagnosis. The subjects were 2964 Japanese patients without a previous diagnosis of primary osteoporosis. We measured bilateral femoral bone mineral density (BMD) and calculated indices, related to the unilateral results, for predicting contralateral hip osteoporosis. A likelihood ratio (LR) of a negative test (LR [-]) of less than 0.2 was considered to exclude the diagnosis. In the normal spinal BMD group, the sensitivity of unilateral DXA for women was 27-73% and LR (-) was 0.28-0.73; the sensitivity for men was 0-50% and LR (-) was 0.51-1.00; the diagnosis of contralateral osteoporosis was not excluded. Sensitivity increased and LR (-) increased with worsening spinal BMD status; however, LR (-) did not meet the cutoff for exclusion. We could exclude unilateral hip osteoporosis, in women only, by performing contralateral femoral DXA; this necessitated lowering the T-score cutoff from -2.5 to -2.0. Unilateral femoral DXA is not useful for excluding the diagnosis of contralateral hip osteoporosis.