A bone mineral density test measures possible bone loss. DEXA (Dual Energy X-ray Absorptiometry) is a type of bone-mineral density test and is considered the "gold standard" in accuracy and precision of bone-density measurement. The X-ray uses two energy levels.  Bones absorb each level differently, and a computer is able to calculate this difference and use it to determine bone density. Bone density measurements focus on bones in the lower spine and both hips, since that is where most osteoporotic fractures occur.

A healthy exterior appearance does not accurately reflect the strength of the bones underneath. While there are many risk factors associated with the development of osteoporosis, the greatest risk is low bone density. Bone density testing is the best way to detect osteoporosis and can help predict risk of fracture.

The amount of X-ray absorbed by the patient is only about 1/10^th of that received from a chest X-ray.

A bone density exam is a simple and comfortable procedure. The bone densitometer looks like a large, padded examination table. The technologist will enter your name, height, weight, age and ethnicity into the computer before your exam. This information is used to compare your results to a normal reference group.

In most case you will remain in your normal clothing, but metal jewelry, belt buckles, and metal or thick plastic buttons will need to be removed from the area being scanned. You will be asked to lie on your back. The technologist will position your arms and legs. The test is painless and takes less than 10 minutes.

A computer analyzes results from the DEXA test by determining how much bone mineral is present. Results are given numerically and graphically and are reported as a T-score and a Z-score.

A T-score result compares your bone density to that of the young adult control group and determines your fracture risk, which increases as your bone density falls below normal:

• A normal T-score is above -1
• An osteopenic result is a T-score between -1 and -2.5
• An osteoporosis result is a T-score that is below -2.5

A Z-score compares your results to people of the same age and body size. Because low bone density is common in older adults, the Z-score can be misleading. Doctors will utilize the T-score in making treatment decisions.

Your healthcare provider might prescribe medication to treat the bone loss identified in your DEXA exam. A repeat DEXA exam in one to two years can help monitor the effectiveness of your treatment.

Bone density testing can be used to establish or confirm a diagnosis of osteoporosis and predict future fracture risk. It is the only sure way to determine bone density. The decision to test for bone density should be based on an individual's risk profile.

The National Osteoporosis Foundation's (NOF) guidelines reference postmenopausal women, but younger women who have several risk factors should discuss bone density testing with their health care providers. Strategies can be started to prevent osteoporosis if bone density testing determines bone loss is occurring. Men at risk for bone loss and osteoporosis can also be tested.

The NOF guidelines recommend bone density testing should be performed on:

• All women aged 65 and older regardless of risk factors
• Younger women who are postmenopausal and have one or more risk factors in addition to being white, female and postmenopausal
• Postmenopausal women who experience fractures (to confirm the diagnosis and determine disease severity)

Medicare covers bone density testing for the following individuals age 65 and older:

• Estrogen-deficient women at clinical risk for osteoporosis
• Individuals with vertebral abnormalities
• Individuals receiving or planning to receive long-term glucocorticoid (steroid) therapy
• Individuals with hyperparathyroidism
• Individuals being monitored to assess the response or efficacy of an approved osteoporosis drug therapy

Medicare permits individuals to repeat bone density testing every two years. Some exceptions do allow for more frequent testing.