Bone Mineral Density Test
A bone mineral density (BMD) test evaluates an individual's bone strength by measuring the density of calcium and other minerals in particular areas of bone. During normal aging, bones lose minerals and become thinner. If they become abnormally thin, however, the patient has a condition known as osteoporosis.
Patients with osteoporosis are in serious danger of fractures. A bone mineral density test can confirm a diagnosis of osteoporosis, assess how well treatment for the disease is working, or predict risk of fracture.
Reasons for Bone Mineral Density Tests
While postmenopausal women are considered at greatest risk for osteoporosis, men aged 50 to 70 are at risk as well. There are many other risk factors for osteoporosis, any of which may be a good reason for a patient of any age or gender to undergo a bone density scan. Risk factors for osteoporosis fall into the following categories: family and medical history of fracture, disease conditions, hormone irregularities and lifestyle habits.
Family and Medical History of Fractures
A family history of osteoporosis or a medical history of previous fractures may be cause for concern, particularly if the patient has suffered a fragility fracture, also known as a stress fracture. A fragility fracture is a bone break caused by minor trauma, such as one believed to have caused a fall rather than resulted from one. Abnormal loss of height, possibly due to compression fractures, must also be taken into consideration.
It is well-known that middle-aged women who are postmenopausal and not taking supplemental estrogen are at risk of developing osteoporosis. A similar risk applies to women who have experienced early menopause, either because of surgery or due to natural causes. Women or men who have had hormone treatment for breast or prostate cancer may also be more vulnerable to osteoporosis.
Many disease conditions make patients more susceptible to osteoporosis. Disorders in this category include rheumatoid arthritis, Type 1 diabetes, liver or kidney disease, thyroid or parathyroid abnormalities, and eating disorders. Individuals with these conditions should undergo regular bone density tests as directed by their physicians. Patients who have taken oral corticosteroids, such as prednisone, to treat any medical condition are also at higher than average risk and should be periodically checked for bone weakness.
Body Build and Lifestyle Habits
Individuals who are have a low body weight, particularly postmenopausal women, should be checked regularly for osteoporosis. Smokers are at increased risk for bone weakness, as are those who drink three or more alcoholic beverages a day. Individuals who are confined to bed should also be watched carefully.
The Bone Mineral Density Procedure
The central DEXA (dual-energy X-ray absorption scan) currently in use to test for bone density is accurate, noninvasive, painless and uses low-dose X-rays. During this test, the patient lies on a table while a scanner is passed over the lower spine and hip. The patient must remain still during the procedure, which takes under an hour. Results are usually available within 2 to 3 days. A smaller version of this procedure is called a peripheral DEXA (p-DEXA); it uses a smaller machine to measure bone density in the hands or feet. These smaller machines are used in doctors' offices, pharmacies and health fairs to provide a quick, but less thorough, evaluation of bone health.
Results of a Bone Mineral Density Test
The results of a bone density scan consist of two scores: one that compares the patient's bone density to that of healthy young women, and one that compares it to individuals of the same age, race and gender as the patient. There are three basic designations given when the results of a bone mineral density test are analyzed. Either the bones have a normal, healthy density, are beginning to lose mass (osteopenia) or have already become weak and porous (osteoporosis).
While a bone density test can confirm whether a patient has low bone density, it does not indicate the reason or exact cause. Additional testing and a complete medical evaluation may be necessary to further investigate the cause of low bone density, so that an appropriate treatment plan may be created.