Bone Densitometry

What is a bone density test?

A bone density test is used to measure the bone mineral content and density. Bone density is tested by dual-energy X-ray absorptiometry (DXA) using special software to determine bone density of the total body, hip, spine or forearm. These procedures are generally done in a clinic, hospital, or free-standing radiology facility. 

This measurement tells the doctor whether there is decreased bone mass, a condition in which bones are more brittle and prone to break or fracture easily.

A bone density test is used mainly to diagnose osteoporosis and determine your fracture risk. The testing procedure typically measures the bone density of the bones of the spine, pelvis, lower arm, and thigh. Portable testing may use the radius (one of the two bones of the lower arm), wrist, fingers, or heel for testing, but is not as precise as the non-portable methods because only one bone site is tested.

Standard X-rays may show weakened bones. But at the point where bone weakness can be seen on standard X-rays, it may be too far advanced to treat. Bone densitometry testing can find decreasing bone density and strength at a much earlier stage when treatment can be beneficial.

Bone density test results

The bone densitometry test determines the bone mineral density (BMD). Your child's BMD is compared to other children of the same age, sex, and race using a statistical measure called the Z-score. The Z-score must be adjusted for your child's height before it can be interpreted. 

• A Z-score of 0 is average
• A Z-score of less than -2 is considered low.
• A Z-score of more than +2 is considered high.

Why might my child need a bone density test?

Bone densitometry testing is primarily performed to monitor bone health in children at risk for the development of osteoporosis. The results are used to help determine what, if any, treatment your child needs to improve the strength of their bones. Early treatment helps to prevent bone fractures.

The complications of broken bones resulting from osteoporosis can be painful and severe. The earlier osteoporosis can be identified, the sooner effective treatment can be implemented.

Bone densitometry testing may also be used to:

• Confirm a diagnosis of osteoporosis if you have already had a bone fracture
• Predict your chances of fracturing a bone in the future
• To determine your rate of bone loss and/or monitor the effects of treatment

There may be other reasons for your doctor to recommend bone densitometry.

What are the risks of a bone density test?

A DXA bone density test is associated with low radiation exposure, much less than a typical X-ray. Nevertheless, you may want to ask your doctor about the amount of radiation used during the procedure and the risks related to your particular situation. It is a good idea to keep a record of your radiation exposure, such as previous CT scans and other types of X-rays, so that you can inform your doctor. Risks associated with radiation exposure may be related to the cumulative number of X-ray examinations and/or treatments over a long period.

There may be other risks depending on your specific medical condition. Be sure to discuss any concerns with your doctor prior to the procedure.

Certain factors or conditions may interfere with a bone density test. These include, but are not limited to, the following:

• Metal jewelry or other metal objects
• Body piercing
• A barium X-ray within 10 days of testing
• Calcified arthritic sclerosis of the posterior vertebrae
• Calcified abdominal aortic aneurysm
• Healed bone fractures
• Metallic clips from previous abdominal surgery
• Recent bone scans

How do I get my child ready for a bone density test?

• Your doctor will explain the procedure to you and ask if you have any questions.
• You will be asked to sign a consent form that gives your permission to do the test. Read the form carefully and ask questions if anything is not clear.
• Generally, no prior preparation, such as not eating or not taking medicine, is needed. You may be told to stop taking calcium supplements 24 to 48 hours prior to your bone density test..
• Based on your child's medical condition, your doctor may give you other instructions on what to do before bone density testing.

What happens during a bone density test?

This test may be done on an outpatient basis or as part of a stay in a hospital. Procedures may vary depending on your child's condition and your doctor's practices.

Generally, it follows this process:

1. In some cases, your child may stay dressed but will be asked to remove all metallic objects, such as belt buckles, zippers, coins, keys, jewelry, dental appliances, and eye glasses. In other cases, he/she will be given a gown to wear so that no buttons, zippers, or hooks will interfere with the imaging process.
2. Your child will be positioned on an X-ray table, lying flat on his/her back. Legs will be supported on a padded box which helps to flatten the pelvis and lumbar spine.
3. Under the table, a photon generator will pass slowly beneath your child, while an X-ray detecting camera passes above the table parallel to the photon generator beneath. Together, they project pictures of the lumbar spine (lower back) and hip bones onto a computer screen. Your child will be asked to stay very still and may be asked to hold his/her breath for a short time in order to get a very clear picture.
4. After the scan of the lumbar spine and hip bones is complete, your child's  foot will be put into a brace that rotates your non-dominant hip (the side you use the least) inward, then the imaging procedure is repeated.
5. The next imaging procedure will involve the radius, one of the two bones of the lower arm. The non-dominant arm (the arm you use the least) is usually examined, unless there is a history of a fracture of that arm.
6. The computer will calculate the amount of photons that are not absorbed by the bones to determine the bone mineral content. The bone mineral density will then be calculated by the radiologist.

The entire scan takes about 30 minutes. A portable scan that checks only your forearm, finger, hand, or foot, takes a bone density reading in a few minutes.

While the bone densitometry procedure itself causes no pain, the movements of the body parts being examined may cause some discomfort or pain, particularly if your chid has recently had surgery or an injury. The technologist will use all possible comfort measures and complete the procedure as quickly as possible to minimize any discomfort or pain.

What happens after a bone density test?

There is no special type of care after a bone density test. Your child may go back your usual diet and activities, unless your doctor advises you differently.

Next steps

Before you agree to the test or the procedure make sure you know:

• The name of the test or procedure
• The reason your child is having the test or procedure
• The risks and benefits of the test or procedure
• When and where your child will have the test or procedure and who will do it
• When and how will you get the results
• How much will you have to pay for the test or procedure