What is a peripheral Bone Density Scan (DEXA)?

Bone density scanning, also called dual-energy x-ray absorptiometry (DXA or DEXA) or bone densitometry, is an enhanced form of x-ray technology that is used to measure bone loss. Peripheral DEXA devices, measure the wrist and forearm, are used for screening purposes.

The main purpose of obtaining a bone density test is determining fracture risk. The bone mineral density correlates very well with risk of fracture. The peripheral devices are good screening tools because of their portability, availability and lower cost, but patients may still need central testing (looking at the hip and lumbar spine), even in light of a normal peripheral test. Your provider will review your results with you and determine if further testing would be indicated.

What are some common uses of the procedure?

Peripheral Dexa testing is recommended if you:

• Women over the age of 40 and have a history of taking progesterone only birth control (ie Norplant, Depo-Provera;
• post-menopausal women, especially those not taking estrogen and those who weigh less than 127 pounds;
• patients with a family history of osteoporosis;
• patients with a history of tobacco smoking;
• patients with a history of moderate alcohol intake;
• patients using medications that are known to cause bone loss, including corticosteroids such as Prednisone, various anti-seizure medications such as Dilantin and certain barbiturates;
• patients with a history of fractures after age of 50 that occurred after only mild trauma.

**The peripheral DEXA is not intended to be used in monitoring the effects of the treatment of osteoporosis and other diseases that result in bone loss.

Women should always inform their provider if there is any possibility that they are pregnant.

How does the procedure work?

The DEXA machine sends a thin, invisible beam of low-dose x-rays with two distinct energy peaks through the bones being examined. One peak is absorbed mainly by soft tissue and the other by bone. The soft tissue amount can be subtracted from the total and what remains is a patient's bone mineral density.

DEXA machines feature special software that compute and display the bone density measurements on a computer monitor.

The pDEXA bone density test is usually completed within 3-5 minutes

Your test results will be in the form of two scores:

T score — This number shows the amount of bone you have compared with a young adult of the same gender with peak bone mass. A score above -1 is considered normal. A score between -1 and -2.5 is classified as osteopenia, the first stage of bone loss. A score below -2.5 is defined as osteoporosis. The T score is used to estimate your risk of developing a fracture.

Z score — This number reflects the amount of bone you have compared with other people in your age group and of the same size and gender. If this score is unusually high or low, it may indicate a need for further medical tests.

Small changes may normally be observed between scans due to differences in positioning and usually are not significant.

What are the benefits vs. risks?

Benefits

• DEXA bone densitometry is a simple, quick and non-invasive procedure.
• No anesthesia is required.
• The amount of radiation used is extremely small—less than one-tenth the dose of a standard chest x-ray.
• pDEXA bone density testing is a convenient method available for the screening of osteoporosis and is also considered an accurate estimator of fracture risk.
• No radiation remains in a patient's body after an x-ray examination.

Risks

• There is always a slight chance of cancer from radiation. However, the benefit of an accurate diagnosis far outweighs the risk.
• The effective radiation dose from this procedure is about 0.01 mSv, which is about the same as the average person receives from background radiation in one day.
• Women should always inform their provider if there is any possibility that they are pregnant.
• No complications are expected with the DEXA procedure.

What are the limitations of a peripheral DEXA Scan?

• A pDEXA test cannot predict who will experience a fracture but can provide indications of relative risk.
• Central DEXA devices are more sensitive than pDEXA devices but they are also somewhat more expensive.
• A test done on a peripheral location, such as wrist, may help predict the risk of fracture in the spine or hip. But because bone mass tends to vary from one location to the other, measuring the wrist is not as accurate as measuring the spine or hip.

Exclusion criteria for the pDexa –

• Individuals who weigh more than 130% of ideal reference weight
• Women who have undergone medical treatment, within the last year, with fluoride, bisphosphonates, or anabolic steroids.
• Women who have undergone medical treatment, within the last 6 months, with estrogen, calcitonin or other drugs known to influence the calcium metabolism.
• Women under 50 who have had both ovaries removed.
• Women who are pregnant
• Individuals with known real disease, secondary osteoporosis caused by tumors, treatment with glucocortiocold steroids, heparin or anti-epileptics, thyroid- or parathyroid disease, malnutrition.
• Heavy smokers/Heavy alcohol intake (more than 20 cigs/day, alcoholics)

Insurance coverage:

Most insurance carriers cover a peripheral dexa scan. You should always check with your insurance regarding what services are covered under your plan. Some plans will only cover a percentage of the cost. The remaining cost will be the responsibility of the patient.