Bone Mineral Density

Bone mineral density is an estimate of bone mass. Bone mineral density tests, such as dual-energy X-ray absorptiometry (DEXA) scans, can be used to estimate the mineral content of bone, and thus its strength and risk for fracture. Osteoporosis is an age-related disease, more prevalent in females, resulting in loss of bone mineral density and associated morbidities, such as fractures. DEXA scan is an accurate and effective method for osteoporosis screening. Early identification of individuals at risk for osteoporosis will allow for therapeutic intervention, which can reduce the risk of osteoporotic-related fractures.

Bone is a dynamic organ and a rich mineral reservoir. It is mainly composed of calcium and phosphorous, and is constantly being broken down and rebuilt. A normal individual has a healthy equilibrium between these two opposing processes. When the mineral content of bone is taken away faster than it is added, the bone becomes thin, weak, and prone to fracture. Bone mineral density tests specifically measure the mineral content of the bone and estimate the risk for fracture.

There are several types of clinical tests that are used to determine bone mineral density. Such tests include the use of single-photon absorptiometry, dual-photon absorptiometry, ultrasound, and quantitative computed tomography. However, the most reliable and accurate test method of predicting fracture risk, while using the least radiation as possible, is the DEXA scan.

A DEXA scan is used to establish the diagnosis of osteoporosis, which places individuals at risk for devastating fractures. In order to determine if a person has osteoporosis, a DEXA scan is performed on the individual's wrists, spine, and hips. The results are [Page 284]then compared to normal cohorts and expressed in two numbers. The Z-score is derived by comparing a person's DEXA scan result to a person of similar age, sex, and race. The T-score is derived from comparing a person's DEXA scan result to that of healthy young adult women. A negative number in either score indicates osteopenia. According to World Health Organization guidelines, a T-score of minus 2.5 establishes the diagnosis of osteoporosis.

An integral part of preventing the morbidities associated with osteoporosis is early patient screening and intervention. General guidelines recommend obtaining a bone mineral density test in all women aged 65 and older, regardless of the presence of any other risk factors for osteoporosis. Younger postmenopausal women who present with one or more risk factors for osteoporosis are also recommended to have DEXA scan screening. Risk factors for osteoporosis include a strong family history of osteoporosis, smoking, early estrogen deficiency, use of medications such as steroids and anticonvulsants, and presence of endocrine abnormalities, such as hyperthyroidism. In addition, postmenopausal women who present with fractures are also recommended to obtain a DEXA scan to confirm the diagnosis of osteoporosis and determine the severity of bone loss. By identifying individuals at greatest risk for osteoporosis and employing early intervention, such as lifestyle modification and medications, the risk of hip and vertebral fractures has been shown to be reduced by up to 50 percent.