Bone mass measurement in identification of women at risk for osteoporosis.

It is now possible to measure bone mass with highly precise, safe and noninvasive technology. Dual energy X-ray absorptiometry (DXA) can detect bone loss well before it becomes evident by conventional X-rays or by fracture. Because measurement of bone density is the single most important predictor of fracture risk, it is a critically important tool to apply to the population at risk, which includes women who have definable risk factors for osteoporosis, such as the menopause, as well as those with a family history of osteoporosis, life-long low calcium intake, smoking, extreme thinness, anorexia, certain diseases and medications. Central DXA machines measure bone mass of the lumbar spine and hip region, the most important potential fracture sites. At the present time, the number of DXA machines in the United States is inadequate to detect the entire population at risk. Even if there were a sufficient number of DXA machines, lack of insurance reimbursement would limit their use. These restraints are beginning to be better defined, if not moderated, by the Bone Mass Measurement Act of 1998. With insufficient numbers of DXA machines and their heavy localization to major urban medical centers, peripheral devices have been developed. Using DXA technology, these peripheral devices can measure densities in the distal forearm, the middle phalangeal bone, and the heel. Ultrasound technology has also been developed to measure bone density of the tibia and the heel. The peripheral densitometers, in general, have the advantage of smaller size, lower cost, and portability. A very controversial issue, however, is whether measurement at a peripheral site provides sufficiently accurate information about bone mass at more important central sites to be generally reliable. Nevertheless, they have great potential in helping to detect the large numbers of women at risk for osteoporosis. Eventually, however, central measurements of bone mass will be needed, especially for monitoring of therapy, so that central measurements of bone mass by DXA are still the "gold standard" in the field at this time.