What is Bone Mineral Densitometry (BMD)?
Bone mineral densitometry (BMD) measures the density (strength) of your bones. It is a way to see if your bones are healthy and strong. There are several different kinds of bone mineral density tests. Dual energy x-ray absorptiometry (DEXA scan) is today’s established standard for measuring BMD.
The bone mineral densitometry machine
How safe is the DEXA scan?
The amount of radiation used for this test is extremely low. It is about the same amount you would get on a long plane flight and less than one tenth the dose of a chest X-ray.
Why should I have a DEXA scan?
To detect osteoporosis, a silent disease. Your bones naturally lose some density, as you get older. The loss of density weakens the bones. Weak bones are prone to fracture. To help prevent such fractures, it is important to diagnose osteoporosis (marked loss of bone density). Osteoporosis can then be treated with proper diet, exercise, and sometimes medicines to help make the bones strong again.
It is also effective in tracking the effects of treatment for osteoporosis.
Who should have a DEXA scan?
It is strongly recommended for anyone, if you are:
- A postmenopausal woman who is at risk (i.e., not on hormone replacement therapy, small body frame, low calcium intake, lack of exercise, smoking ).
- A man with clinical conditions associated with bone loss.
- On medications known to cause bone loss including corticosteroids, antiseizures medications such as dilantin or high dose thyroid replacement drugs.
- Have type one diabetes, liver disease, kidney disease, hyperthyroidism or a family history of osteoporosis.
- Have experienced a fracture after only a mild trauma.
- Have had evidence of vertebral fracture or other signs of osteoporosis.
How can I prepare for the DEXA scan?
On the day of examination, eat normally, but don’t take calcium supplements for at least 24 hours beforehand.
Inform your doctor if you recently had a barium examination or have been injected a contrast material for a computed tomography (CT) scan or radioisotope scan, you may have to wait 10-14 days before undergoing a DEXA test.
Women should always inform the doctor and radiographer if there is a possibility they are pregnant.
How is a DEXA scan done?
During the scan you will lie down on a padded table with an “arm” suspended overhead. It’s important that you stay as still as possible during the procedure to ensure a clear, useful image. The DEXA machine sends a thin, invisible beam of low dose x-rays through your bones and images are generated on a computer monitor. It is quick and painless. It takes just a few minutes to check the bone density of your spine and hip. (The hip and spine are the most common areas checked because they are most prone to fracture if your bones are weakened).
A subject is undergoing a bone mineral densitometry testing
What happens after the scan?
There is actually nothing much to anticipate after the scan. You may return to your normal routine and diet.
Are there any possible complications?
No complications are expected with the DEXA scan.
What information can be obtained from the DEXA scan?
A panel of World Health Organization (WHO) experts has developed categories that define the amount of bone loss:
- Normal: A T-score that is above -1
- Osteopenic (the first stage of bone loss): A T-score between -1 and – 2.5
- Osteoporosis: A T-score below -2.5
The result has to be interpreted along with your overall health, your risk factors for osteoporosis, and your lifestyle. A diagnosis of osteoporosis cannot predict a bone fracture, it simply means the risk of having a fracture is higher than that of normal bones. Your doctor will take all of these factors into account before deciding whether you may need medicine to restore the bone density.
What are the limitations of DEXA scan?
It is of limited use in people with a spinal deformity or those who have had previous spinal surgery. The presence of vertebral compression fractures or osteoarthritis may interfere with the accuracy of the test.
Disclaimer: This is only general information. A doctor should be contacted if you need any medical advice or if medical decisions need to be made.