What is a bone mineral density (BMD) test?

Following a comprehensive medical assessment, your doctor may recommend a bone mineral density (BMD) test to measure bone density in the spine, wrist and/or hip. These are the most common sites of fracture because of osteoporosis, a disorder in which bones gradually become thinner and weaker. Other tests measure bone in the heel or hand. The tests are painless, noninvasive and safe.

Why would I need a BMD test?

Women age 65 and older should be screened routinely for osteoporosis, according to the U.S. Preventive Services Task Force (USPSTF). However, routine screening should start at age 60 for women at increased risk for osteoporotic fractures. Other organizations offer guidelines that differ somewhat.

Many women are unaware that they have low bone densities or osteoporosis until they suffer a fracture. The USPSTF has found that low body weight is the single best predictor of low bone mineral density.

A BMD may also be recommended for perimenopausal women who have a family history of osteoporosis, adhere to a low-calcium diet, drink alcohol and/or smoke, have low body weight or are physically inactive and have other risk factors.

A BMD can:

• Detect osteoporosis before a fracture occurs.
• Confirm a diagnosis of osteoporosis if you have already suffered a fracture.
• Predict your chances of developing a fracture in the future.
• Determine your rate of bone loss, and/or monitor the effects of treatment if the test is conducted at intervals of a year or more.

How is bone density measured?

Bone density is measured through painless, noninvasive scanning techniques based on x-ray radiation. These techniques require you to be positioned for the scan and to hold still while it is being completed. Specific methods are:

• Dual energy x-ray absorptiometry (DEXA) measures the spine, hip or total body, and is the most widely used technique available. The procedure exposes the patient to little radiation, needs little scanning time, is inexpensive and is highly accurate. Because of its precision, DEXA is well suited to making serial (repeated) measurements. Serial bone density measurements may be done to track bone loss over time, to evaluate the effectiveness of treatment or as part of a clinical trial for a new potential treatment for osteoporosis.



• Peripheral dual energy x-ray absorptiometry (DEXA), which also uses dual energy absorptiometry, measures the bone content of the peripheral skeleton, specifically the wrist, finger or heel.



• Single energy x-ray absorptiometry (SXA) measures the wrist or heel bone density.



• Single photon absorptiometry (SPA) measures the wrist bone density (used infrequently).



• Dual photon absorptiometry (DPA) measures the spine, hip or total body bone density (used infrequently).



• Quantitative computed tomography (QCT) is most commonly used to measure the spine, but can be used to measure bone density in other parts of the body as well. QCT exposes the patient to much higher levels of radiation than "regular" CT. For this reason, it should not be used for women of childbearing age, or for repeated measurements in the same patient.



• Radiographic absorptiometry (RA) uses a special x-ray technique of the hand to calculate bone density.

How do I prepare for an exam?

Wear comfortable clothing with no metal zippers, buttons or buckles. Also, remove your jewelry or metal items beforehand. A brief medical history is required, which may include: family history of osteoporosis, radiographic findings of osteoporosis, recent fractures and post-menopause or early menopause information.

Let the bone density technologist know if you are pregnant or think you may be; have any metal implants inside your body or recent fractures; have had a recent nuclear medicine scan or a barium enema.

What can I expect during my exam?

This depends on what type of scan you are having. If you are having a DEXA bone density scan, you will be asked to lie on a table or sit down. The scanner arm will move back and forth over the part of your body being scanned. Typical DEXA exams are completely painless and only take 10 minutes to perform.

If you are having your heel bone scanned, you put your foot into a small box, where the sound waves penetrate the heel bone for 10 seconds.

What do the results mean?

Your bone density is compared to two standards known as age-matched and young normal. Age-matched compares your bone density to what is expected for someone your age, sex and size. Young normal compares your density to the optimal peak bone density of a healthy young adult of the same sex. The results enable your doctor to identify where you stand within ranges of normal and to determine whether you are at risk for a fracture. As a rule, the lower your bone density, the higher your risk for fracture. Once your bone density is determined, your physician can advise you on how to best maintain and/or improve your bone density.