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 non-portable 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.
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.
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 physician 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.
Reasons for the Procedure
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.
There may be other reasons for your physician to recommend bone densitometry.
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.