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A quiz in JAMA uses a case with discordant DXA results to discuss the options in assessment of hip fracture risk in osteoporosis, describing their advantages and drawbacks.
Neuner J, Carnahan J. Dual X-ray Absorptiometry for Diagnosis of Osteoporosis. JAMA (2014) 312:1147-1148. doi:10.1001/jama.2014.1402. Online September 17, 2014
This quiz uses dual x-ray absorptiometry (DXA), in the context of the United States Preventive Services Task Force (USPSTF) recommendations, to evaluate a patient, develop a treatment plan, and explain the benefits of therapy to the patient.
The patient is a white woman, 69, with discordant T Scores. The spinal T Score, -3.1, is in the osteoporosis range, but the femoral neck T Score, -2.1, is not. A T score of -2.5 is only 64% sensitive and 84% specific for hip fracture risk, and fewer than half of women with hip fractures actually had osteoporosis.
By expert consensus, osteoporosis is diagnosed in postmenopausal women when either a central (spine or femoral neck) DXA is ≥2.5 standard deviations below a young adult reference mean (T score <2.5), and other causes of low bone density are excluded. So she is diagnosed with osteoporosis.
The text discusses the details of recommended alternative testing methods, including their drawbacks.
In this case, the patient's fracture risk was calculated at 5 times that of a young healthy women. The answer reveals her adjusted osteoporotic fracture risk, compares it with the risk after alendronate treatment, and reveals what happened.