Dual-energy x-ray absorptiometry (DEXA)

1. Uses x-rays at two energy levels to determine the bone mineral content.
2. Major role in diagnosis of osteoporosis, the assessment of patients' risk of fracture, and monitoring response to treatment.
3. T-score is a number of standard deviations between the patient’s mean BMD and the mean of the population compared with reference populations matched in gender and race.
4. Z-score is the number of standard deviations above or below the mean of age-matched controls.
5. DEXA could be used to measure bone density at many skeletal sites, two sites are typically measured: the first four vertebrae of the lumbar spine posteroanterior, and the proximal femur (“hip”), including the femoral neck and the trochanteric areas and total hip measurement. Femoral neck and lumbar spine are the gold standard for evaluating osteoporosis, with good accuracy and high precision.
6. All women 65 years and older and men 70 years and older should be screened for asymptomatic osteoporosis.

The World Health Organization (WHO) defines T-scores as:

• Greater than or equal to -1.0: normal
• Less than -1.0 to greater than -2.5: osteopenia
• Less than or equal to -2.5: osteoporosis
• Less than or equal to -2.5 plus fragility fracture: severe osteoporosis

Clinical risk factors included in WHO fracture algorithm

• Age
• Low body mass index
• Prior fracture after age 50
• Parental history of hip fracture
• Current smoking habit
• Current or past use of systemic corticosteroids
• Alcohol intake >2 units daily
• Rheumatoid arthritis