(Bone Mineral Density [BMD] Test, Bone Density Test, Bone Mineral Content, Bone Absorptiometry)
Bone densitometry is used to measure the 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 free-standing radiology facility.
However, for mass screening purposes, there are portable types of bone densitometry testing. The portable testing is done using either a DEXA (or DXA) 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 the bone mineral density (BMD). Your BMD is compared to two norms--healthy young adults (your T-score) and age-matched (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 (SD) 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.
According to the World Health Organization, osteoporosis is defined based on the following bone density levels:
In general, the risk for bone fracture doubles with every SD below normal. Thus, a person with a BMD of 1 SD below normal (T-score of -1) has twice the risk for bone fracture as a person with a normal BMD. A person with a T-score of -2 has four times the risk for bone fracture as a person with a normal BMD. When this information is known, people with a high risk for bone fracture can be treated with the goal of preventing future fractures. Severe (established) osteoporosis is defined as having a bone density that is more than 2.5 SD below the young adult mean with one or more past fractures due to osteoporosis.
Secondly, your BMD is compared to an age-matched norm. This is called your Z-score. Z-scores are calculated in the same way, but the comparisons are made to someone of your age, sex, race, height, and weight.
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, and/or assess the levels of minerals in the body related to bone strength, such as calcium.
Other related procedures that may be used to diagnose bone problems include bone scan and X-rays of the bones. Please see these procedures for more information.
Bone densitometry testing is primarily performed to identify persons with osteoporosis and osteopenia (decreased bone mass) 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:
There may be other reasons for your doctor to recommend bone densitometry.
Osteoporosis is most commonly found in postmenopausal women, where the absence of the hormone estrogen is related to the loss of bone mass. Other conditions that may cause osteoporosis or osteopenia include, but are not limited to, the following:
These conditions affect bone formation due to problems with absorption of certain substances, such as Vitamin D and calcium, which are needed to form strong bones.
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 and/or treatments over a long period of time.
If you are pregnant or suspect that you may be pregnant, you should notify your doctor. 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:
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:
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.
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 disease, or replace the professional medical advice you receive from your doctor. Please consult your health care provider with any questions or concerns you may have regarding your condition.
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