How Do I Know If I Have Osteoporosis?
Testing for bone loss

Osteoporosis is diagnosed by measuring bone density. If you are over age 65, if you are a postmenopausal woman who has had a bone fracture, if you are a woman on prolonged hormone replacement therapy, if you are anorexic (eating disorder) or do not have a monthly menstrual cycle, or if you take steroids for any illness, you should have a bone density test. Ideally, you should measure your bone mass and begin prevention techniques or treatment to stop bone loss before bone density has decreased to the point where fractures occur. Early testing can mean the difference between a prevention program, such as taking calcium supplements with vitamin D, and a treatment program such as hormone replacement therapy. While you are at your doctor's office, you may have an x-ray to determine bone density or your doctor may recommend a testing facility. Testing is often done at a diagnostic outpatient facility or at a hospital.

What tests are available?
There are several types of noninvasive, painless tests available to measure bone mineral density. These tests are used not only to diagnose osteoporosis but also to follow the effectiveness of treatment. The test can measure bone density in your spine, hip, or wrist- the most common areas for fractures from osteoporosis. Once your bone density is known, it is compared against two standards, known as the age-match reading and the young-normal reading. The age-match reading compares your bone density to what is expected in someone of your age, sex, and size. The young-normal reading compares your density to the optimal peak bone density of a healthy young adult of the same sex and size. Using these comparisons, your doctor can determine whether you are at risk for a fracture and what action should be taken to avoid osteoporosis-related fractures.

The most common testing method in use today is Dual-Energy X-ray Absorptiometry (DEXA), also known as a Dual X-ray Absorptiometry (DXA) scan (Fig.). This test has very little radiation; it is precise; and it can measure the bone density of the spine, hips, or the entire body. The test is simple and takes only a few minutes. It is fairly expensive, however, averaging about $300.

Radiographic Absorptiometry (RA) is less expensive and more mobile, but it only uses an x-ray of the hand to calculate bone density. The Quantitative Computed Tomography (QCT) is most often used to measure the spine but it can also measure other sites. The QCT is also sensitive to early bone loss. Unfortunately, it has a high radiation level and limited access. Other less frequently used screening tests include the Single X-ray Absorptiometry (SXA), which measures the wrist or heel, and the Quantitative Ultrasound (QUS), which uses sound waves to measure the spine and other sites. Peripheral screening tests, such as the pDEXA and Peripheral Ultrasound that measure the wrist and heel, have a limited screening area and are less sensitive; however, they are also less expensive and more mobile, which makes them more accessible.

Conventional x-ray can be used for screening, but it is subject to some significant limitations. An x-ray does not show bone loss until as much as 25% of your bone is gone and an x-ray is technique dependent. For example, if the x-ray taken is not of good guality, the doctor may not be able to tell for certain if osteopenia (thinning of the bone from age) or osteoporosis is present.

Bone density testing is recommended for all women over the age of 65, but you may want to be tested earlier if you are postmenopausal or have other risk factors for osteoporosis. Men should also be screened if they have any risk factors. Typically, scans are performed every 2 years. Testing more frequently is usually not helpful because the rate of bone loss or gain is so slow that it takes at least 1 year to see any results or changes.

Kristyn Fagerberg, MD
Columbus, Georgia