Bone densitometry is used to measure bone mineral content and density. This measurement can indicate decreased bone mass, a condition in which bones are more brittle and more prone to break or fracture easily. Bone densitometry is used primarily to diagnose osteoporosis and to determine fracture risk. The testing procedure measures the bone density of the bones of the spine, pelvis, lower arm and thigh.
Bone densitometry testing may be done using X-rays, dual-energy X-ray absorptiometry (DEXA or DXA) or by quantitative CT scanning using special software to determine bone density of the hip or spine. These procedures are generally done in a clinic, hospital or freestanding radiology facility.
However, for mass screening purposes, there are portable types of bone densitometry testing. The portable testing is done using either a DEXA X-ray device or a quantitative ultrasound unit. Both types of portable testing may use the radius (one of the two bones of the lower arm), wrist, fingers or heel for testing. The portable testing, while useful for general screening, is not as precise as the nonportable methods because only one bone site is tested.
Standard X-rays may detect weakened bones. However, at the point where bone weakness is obvious on standard X-rays, the bone weakness may be too far advanced for treatment to be effective. Bone densitometry testing can determine decreasing bone density and strength at a much earlier stage, when treatment of the bone weakness can be beneficial.
The bone densitometry test determines bone mineral density (BMD). Your BMD is compared to two norms: healthy young adults (your T-score) and age-matched adults (your Z-score).
First, your BMD result is compared with the BMD results from healthy 25- to 35-year-old adults of your same sex and ethnicity. The standard deviation is the difference between your BMD and that of the healthy young adults. This result is your T-score. Positive T-scores indicate the bone is stronger than normal; negative T-scores indicate the bone is weaker than normal.
Peoples Health recommends that women age 65 and over – as well as younger women with one or more risk factors – receive a bone mineral density test to establish a baseline. This will help a doctor advise a woman on how often she should receive subsequent tests. Peoples Health also recommends any woman age 65 and older receive a test within six months of the date of suffering a fracture.
In addition to bone densitometry testing, your doctor may recommend other types of tests, such as blood tests, which may be used to detect the presence of renal (kidney) disease, evaluate the function of the parathyroid gland, evaluate the effects of cortisone therapy, or assess the levels of calcium and other minerals in the body related to bone strength.
Other related procedures that may be used to diagnose bone problems include bone scans and X-rays of the bones.
Reasons for the procedure
Bone densitometry testing is primarily performed to identify persons with osteoporosis and osteopenia (decreased bone mass that has not reached the level of osteoporosis) so that the appropriate medical therapy and treatment can be implemented. Early treatment helps to prevent future bone fractures. It may also be recommended for persons who have already had a fracture and are considered at risk for osteoporosis.
The complications of broken bones resulting from osteoporosis are often severe, particularly in the elderly. The earlier osteoporosis can be identified, the sooner effective treatment can be implemented, thus most likely lessening the severity of the condition.
Bone densitometry testing may also be used:
To confirm a diagnosis of osteoporosis if you have already had a fracture
To predict your chances of fracturing in the future
To determine your rate of bone loss or monitor the effects of treatment
There may be other reasons for your doctor to recommend bone densitometry.
Risks of the procedure
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 past history of radiation exposure, such as previous 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 or treatments over a long period of time.
If you are pregnant or suspect that you may be pregnant, you should notify your healthcare provider. Radiation exposure during pregnancy may lead to birth defects.
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 bone densitometry testing. These include, but are not limited to, the following:
Metal jewelry or other metal objects
A barium X-ray within 10 days of testing
Healed bone fractures
Metallic clips from previous abdominal surgery
Recent bone scans
Before the procedure
Your provider will explain the procedure to you and offer you the opportunity to ask questions about the procedure.
Generally, no prior preparation, such as fasting or sedation, is required. However, you may be advised to stop taking calcium supplements 24 to 48 hours prior to your bone density test.
Notify the technologist if you are pregnant or suspect you may be pregnant.
Based on your medical condition, your doctor may request other specific preparation.
During the procedure
Bone densitometry testing may be performed on an outpatient basis or as part of your stay in a hospital. Procedures may vary depending on your condition and your doctor's practices.
Generally, bone densitometry follows this process:
In some cases, you may stay dressed but will be asked to remove all metallic objects, such as belt buckles, zippers, coins, keys and jewelry. In other cases, you will be given a gown to wear so that no buttons, zippers or hooks will interfere with the imaging process.
You will be positioned on an X-ray table, lying flat. Your legs will be supported on a padded box, which serves to flatten the pelvis and lumbar spine.
Under the table, a photon generator will pass slowly beneath you, while an X-ray detector camera will pass above the table parallel to the photon generator beneath, projecting images of the lumbar and hip bones onto a computer monitor.
After the scan of the lumbar and hip bones is complete, your foot will be inserted into a brace that moves your nondominant hip (the side you use the least) into an internally rotated position, and the previous imaging procedure is repeated.
The next imaging procedure will involve the radius, one of the two bones of the lower arm. The nondominant arm (the arm you use the least) is usually examined, unless there is a history of a fracture of that arm.
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.
While the bone densitometry procedure itself causes no pain, the manipulation of the body part being examined may cause some discomfort or pain, particularly in the case of a recent injury or invasive procedure, such as surgery. The technologist will use all possible comfort measures and complete the procedure as quickly as possible to minimize any discomfort or pain.
After the procedure
There is no special type of care following bone densitometry testing. You may resume your usual diet and activities, unless your doctor advises you differently.
The content provided here is for informational purposes only and was not designed to diagnose or treat a health problem or replace the professional medical advice you receive from your doctor. Please consult your healthcare provider with any questions or concerns you may have regarding your condition.
This page contains links to other websites with information about this procedure and related health conditions. We hope you find these sites helpful, but please remember we do not control or endorse the information presented on these websites, nor do these sites endorse the information contained here.
American Academy of Orthopaedic Surgeons
Foundation for Osteoporosis Research and Education
National Institute of Child Health and Human Development
National Institutes of Health (NIH)
National Library of Medicine
National Osteoporosis Foundation
NIH - Osteoporosis and Related Bone Diseases - National Resource Center