What is DEXA scan or Bone mineral densitometry (BMD)?
DEXA scan (dual energy x-ray absorptiometry) or bone mineral densitometry (BMD) uses a special type of X-ray to measure your bone density. Reduced bone density can lead to the weakening of bones and fractures. This condition is called osteoporosis and is more common in women after menopause. DEXA scan is the best available test for the diagnosis of osteoporosis and used to predict the risk of fracture.
Preparation for the test
Do not take calcium or vitamin tablets before the procedure
Who should be tested?
- Anyone with a previous fracture caused by normal activities or following a trivial fall.
- All women older than 65 and men older than 70
- Postmenopausal women between 50 and 65, with risk factors for osteoporosis
- Men aged 50 to 69, with risk factors for osteoporosis
- Thin build (body weight less than 127 pounds or 58 kg, body mass index less than 21)
- Parent with a hip fracture
- Current smoker
- Alcohol intake more than 3 drinks on most days
- Rheumatoid arthritis
- Early menopause
When should you be retested?
A repeat test is indicated when it is likely to influence your clinical management. Consider repeating the test in one to two years if your doctor as started medications to treat your osteoporosis. Depending on some preexisting risk factors, your doctor may advise you to undergo repeat testing even sooner. You should discuss this with your doctor. If your first test was normal, you should wait at least 2 years or more before repeating the test.
Meaning of the test results
The test results are reported in T and Z scores. T score compares your current bone density with that of a normal, healthy young adult population of the same gender. T score is used to define osteoporosis in postmenopausal women. Z score compared your current bone density with that of a population of the same age, gender and race. Z scores are useful in premenopausal women under the age of 50.
- Normal: less than a standard deviation below normal (greater than -1).
- Osteopenia:1 to 2.5 standard deviations below normal (-1 to -2.5).
- Osteoporosis: greater than 2.5 standard deviations below normal (less than -2.5)
Discuss your test results with your doctor. The doctor will use this information, along with other parameters to determine your fracture risk. If you already have been diagnosed with osteoporosis, DEXA is useful to monitor the progress of your treatment.