DUAL ENERGY X-RAY ABSORPTIOMETRY (DEXA)
Dual energy x-ray absorptiometry (DEXA), assesses total body bone mineral density and highly accurate measures of the body’s soft tissue composition (muscle mass and fat mass). By measuring your body’s muscle mass, fat mass, and bone mineral density, Measure Up can determine your total body fat percentage, and changes in regional body composition.
A dual energy X-ray absorptiometry (DXA or DEXA) scan measures your bone density. It can look for signs of fragile (brittle) bones to assess your risk of a fracture (break).
You will meet the radiographer carrying out your procedure to discuss your care. It may differ from what is described here as it will be designed to meet your individual needs.
A DXA scan uses X-ray equipment and a computer to measure the density of your bones.
A DXA scan projects X-rays onto your bones. Some of this radiation travels straight through your bones and a certain amount is absorbed by them. How much is absorbed depends on how dense your bones are. A device called a detector measures how much radiation passes through your bones and it sends the information to a computer. This works out an average bone density score. Your score will be compared with normal measurements for both a young, healthy adult, and to people your own age, size and gender. Low scores indicate that your bones are fragile and more likely to fracture.
Doctors use DXA scans to assess your risk of developing osteoporosis. This is a condition where your bones lose their density and become weak, brittle and more likely to fracture. Your doctor may advise you to have a DXA scan if you fracture a bone after only a minor bump or fall. You may also need to have a DXA scan if you’re at a high risk of osteoporosis. Doctors also use DXA scans to monitor how well you respond to treatment for osteoporosis.
You may need to have a DXA scan if you have another health condition that can affect the density of your bones. These include eating disorders, such as anorexia nervosa, and kidney disease.
A DXA scan is quick and painless, and both adults and children can have the scan.
DEXA SCAN PREPARATION
- No prior radionuclide studies for 2 weeks
- No barium contrast studies for 2 weeks
- No metal in clothing (i.e. zippers)
HOW IS A DEXA SCAN DONE?
You lie on your back on a couch and are asked to keep still while an X-ray detector (the ‘scanner’) comes over the area to be tested. An X-ray machine fires X-rays towards the detector. The bones commonly scanned are the vertebrae (back bones), hip and wrist. (These are the bones that most commonly fracture due to osteoporosis.) The scan usually takes between 10 and 20 minutes, depending on which part of your body is being examined, and whether a central or peripheral scanner is being used. Peripheral scanners are available in some GP surgeries and can be used to check the bone mass density of the heel, wrist or finger. You do not need to do any special preparation prior to a DEXA scan.
WHO SHOULD HAVE A DEXA SCAN?
A DEXA scan may be advised if you are at increased risk of osteoporosis. Osteoporosis usually causes no symptoms at first. However, if you have osteoporosis, you have an increased risk of breaking a bone. (See separate leaflet called Osteoporosis for more details.) If a DEXA scan shows that you have osteoporosis, then you may be given advice and treatment to help strengthen your bones. Therefore, a
DEXA scan may be advised if you have:
- A fracture following a minor fall or injury.
- Loss of height due to fracture of a vertebra (back bone).
- Taken steroid tablets for three months or more.
- An early menopause (aged less than 45).
- A history of periods stopping (amenorrhoea) for more than one year before the menopause.
- Other disorders associated with osteoporosis such as rheumatoid arthritis or coeliac disease.
- A family history of hip fracture on your mother’s side of your family.
- A body mass index of less than 19 (that is, if you are very underweight.)
WHEN CAN I EXPECT THE RESULTS OF MY BMD (DEXA) SCAN?
The time that it takes your doctor to receive a written report on the test or procedure you have had will vary, depending on:
- the urgency with which the result is needed;
- the complexity of the examination;
- whether more information is needed from your doctor before the examination can be interpreted by the radiologist;
- whether you have had previous X-rays or other medical imaging that needs to be compared with this new test or procedure (this is commonly the case if you have a disease or condition that is being followed to assess your progress);
- whether or not you have had a previous BMD scan, so that the results can be compared;
- how the report is conveyed from the practice or hospital to your doctor (i.e. phone, email, fax or mail).
Please feel free to ask the private practice, clinic, or hospital where you are having your test or procedure when your doctor is likely to have the written report.
It is important that you discuss the results with the doctor who referred you, either in person or on the telephone, so that they can explain what the results mean for you.