Dual X-ray Absorptiometry (DXA)

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A DXA scan, or dual x-ray absorptiometry, is a fast and painless test performed to measure bone density – the strength of the bones.  Not only can the test diagnose osteoporosis, but is used to detect early stage bone loss (osteopenia).  A DXA scan, also called bone densitometry, may be repeated to measure the success of treatment to prevent osteoporosis. The result of the test is called the T-score which is useful for physicians planning treatment.

Who may need DXA?

DXA is used to diagnose osteoporosis and low bone density. While anybody can develop osteoporosis or low bone density, certain groups are at particular risk:

Women

Post-menopausal, not taking estrogen replacement therapy

• Thin or with a small frame

Men and Women

Family history of osteoporosis

• Smoker
• Corticosteroid use
• Certain anti-seizure drug use
• Type 1 diabetes, liver or kidney disease, thyroid/parathyroid disorder
• Previous fracture, especially with mild trauma

What is a DXA machine?

DXA is the newer technology previously known as DEXA (or dual energy x-ray absorptiometry).  DXA and quantitative CT (computed tomography) are used to measure bone density in the spine and hip.  This type of testing is preferred over peripheral or similar machines (pDEXA) that only measure bone density of the finger, wrist, or heel.

Test Preparation

Other than delaying calcium supplementation until after the test, no special preparation is necessary. Patients do not need to disrobe but must remove metallic jewelry or metallic items (such as a belt buckle).

Procedure

The patient lies flat on a padded table. The technician may place cushions to prop the body into position or make the patient more comfortable. Radiation exposure is minimal and the test is over within 10 minutes.

The T-score

The T-score is determined by comparing the patient’s bone density to the bone density of an average young adult.  The score is further computed by determining the number of standard deviations of the patient’s bone density above or below the standard. Physicians can use a T-score to assess bone health, plan treatment, and assess risk of fracture (and develop preventive treatments).