Bone Density Scan
What is "bone mineral density" (BMD)?
Bone mineral density (BMD) testing generally correlates with bone strength and is used to diagnose osteoporosis. The BMD is measured with a dual energy x-ray absorptiometry test (referred to as a DXA scan). By measuring BMD, it is possible to predict fracture risk in the same manner that measuring blood pressure can help predict the risk of stroke.
It is important to remember that BMD cannot predict the certainty of developing a fracture. It can only predict risk. It is important to note that a bone density scan, or test, should not be confused with a bone scan, which is a nuclear medicine test that is used to detect tumors, cancer, fractures, and infections in the bone.
Weight loss and bone loss can sometimes go hand in hand. Doctors know that women with anorexia, who severely restrict calories for a long time, are at increased risk for osteoporosis. The eating disorder interferes with hormones needed to maintain bone, not to mention the foods people need to build bone. But what if you don’t have anorexia? What’s the relationship between osteoporosis and normal dieting? How do you know if you’re at risk for bone loss? What kind of dieting is safe for your bones? Those...
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The World Health Organization is the source of the commonly accepted definitions for osteoporosis (WHO Technical Report Series #843, Geneva 1994):
Normal: A value for BMD statistically within 1 standard deviation of the young adult peak bone mass. The report shows a T score between +1 and -1, signifying a BMD within the normal range.
Low bone mass (medically termed osteopenia): A value for BMD greater than 1 standard deviation but less than 2.5 standard deviations below that of an average young adult. The report shows a T score between -1 and -2.5, which signifies an increased fracture risk but does not meet the criteria for osteoporosis.
Osteoporosis: A value for BMD 2.5 or greater standard deviations below that of the average peak young adult bone mass. BMD in this range signifies an even higher fracture risk than osteopenia. The report shows a T score of -2.5 or lower.
The National Osteoporosis Foundation estimates that 10 million people in the U.S. have osteoporosis and nearly 34 million more have osteopenia, which puts them at greater risk for osteoporosis.
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