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Bone density scan
A bone density scan is an imaging test that uses x-rays and computer technology to measure bone density. A bone density scan is also called a bone densitometry or dual energy x-ray absorptiometry (DXA) scan.
Why a bone density scan is done
A bone density scan is done to:
- measure the amount of minerals, such as calcium, in bone
- assess a person’s risk of bone fractures
- check for bone loss
Bone loss can result from:
- certain treatments, such as
- hormonal therapies
- radiation to weight-bearing bones
- some chemotherapy drugs
- some anti-seizure drugs
- long-term use of blood thinners
- certain conditions, such as
- early menopause
- low testosterone level in men
- thyroid or parathyroid disorders
- long periods of bed rest and not being active
- increasing age
- bone marrow transplant
Osteoporosis is a condition in which the bone mineral density is lower than normal. The risk factors for osteoporosis include:
- high alcohol intake
- high caffeine intake
- sedentary lifestyle
- diet low in calcium or vitamin D
- family history of osteoporosis
- history of fractures occurring with minimal trauma
- low body weight or weight loss
How a bone density scan is done
A bone density scan is usually done as an outpatient procedure in the x-ray (radiology) department of a hospital or clinic. Depending on the number of areas being scanned, the test takes between 5 and 20 minutes.
- It is important for women to tell the x-ray technologist or radiologist if they are pregnant, or think they may be pregnant, before having any type of x-ray.
- The person can eat normally, but should not take calcium supplements for 24 hours before the test.
- The person may be asked to wear clothing that has no metal zippers, belts or buttons. They may be asked to change into a gown during the test and remove glasses, jewellery or objects that could interfere with the test.
During the test:
- The person lies on a table and is placed in position. The person must lie still while the scan is being done.
- The scanner moves over the area to be scanned and uses low-dose x-rays to produce images on a computer screen.
- X-rays are taken of the bones of the lower spine and hip.
- Sometimes x-rays are also taken of the forearms.
- In some cases, the whole body is measured.
Potential side effects
X-rays involve low levels of ionizing radiation, which has the potential to cause cancer and other defects. As with any x-ray test, there is some radiation exposure, but the amount from a bone density scan is very little (less than one-tenth the amount of radiation used in a chest x-ray) and poses no danger.
X-rays are strictly monitored and controlled to make sure they use the smallest amount of radiation possible. The expected benefits of the x-rays must always outweigh any possible risk for the x-rays to be done.
What the results mean
Bone density scan results tell the doctor how dense the bones are. The way in which the results are used depends on the age of the person. A bone density scan does not tell a person that they will have a bone fracture, but it provides an idea about how great their risk is.
For people over age 50, the results of the bone density scan are combined with age, gender, history of certain fractures and history of using a glucocorticoid (for example, prednisone). Together, these factors are used to determine a person’s chance of breaking a bone over the next 10 years. Risk is classified as:
- low – The risk of fracture is less than 10%.
- moderate – The risk of fracture is between 10% and 20%.
- high – The risk of fracture is over 20%.
For people under 50 years of age, absolute risk is not determined. Instead, their results are compared to values that would be expected for a young, healthy person and are classified as being either normal or reduced.
What happens if a change or abnormality is found
The doctor will decide whether further tests, procedures, follow-up care or treatment to manage bone loss are needed.
Special considerations for children
Being prepared for a test or procedure can reduce anxiety, increase cooperation and help the child develop coping skills. Parents and caregivers can help prepare children by explaining to them what will happen, including what they will see, feel and hear during the test.
- The child will probably be alone in the room.
- The child needs to lie still on the table.
- Younger children may need sedation or general anesthesia to relax and lie still if CT or MRI is being used
- Special preparation may be needed if sedation or a general anesthetic is used.
- Children may not be allowed to eat or drink for several hours before the test.
- An IV may be put into a vein in the hand or arm.
- Children may be put on a heart monitor.
The preparation you can provide for this test depends on the age and experience of the child. See the following for more age-specific information on helping children cope with tests and treatment.