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Bone Density: A Clue to Your Future

DEXA bone density scans: Will you glide into your golden years or live out a fractured fairy tale?

The Bone Density Test Itself

At least nine different methods are used to measure bone density, according to the National Osteoporosis Foundation, but the most commonly used test is called Dual Energy X-ray Absorptiometry or DEXA. It measures the bone mass at the spine, hip, or total body.

The bone density test is totally noninvasive, says Kim Templeton, MD, an associate professor of orthopaedic surgery at the University of Kansas. "There are no injections," Templeton says. "You lay on a table and the scanner scans you. The hardest part is lying there, for about 15 to 20 minutes." The average cost is about $150, says Templeton.

And a bone density scan is not the same as a bone scan, Templeton says, although women often mix up the two. A bone scan is a kind of nuclear medicine test in which a radioactive tracer is injected into a vein so the doctor can scan the body, looking for bone tumors or other problems such as infection.

Bone Density Scans: Your Results

The bone density test produces two scores: the T score and The Z score.

"The T score looks at the amount of bone you have compared to someone with peak bone mass (a 30-year-old healthy adult)," Templeton says. "The Z score is looking at someone your age and your same gender, to find out how you stack up with people your own age."

A T score of minus one and higher is normal, Templeton says. "Osteopenia(bone mass lower than normal peak bone mass) is below minus one to minus 2.5. Lower than minus 2.5 is osteoporosis."

A negative Z score means you have thinner bones than the average of others in your age group; positive means you have better.

If your Z score is lower than others your age, it can be a tip-off, Templeton says, that something else is medically happening. "It may not be anything serious," she says. "Maybe you're not getting enough vitamin D."

The Bone Density Test Reality

Like other medical tests, the bone density test isn't perfect. While it can help predict who will have a fracture, and may need treatment or lifestyle changes, it's not foolproof. And, Templeton says, experts have discovered recently that the bone's architecture -- how well your bones are put together -- may also play an important role in predicting fractures.

"If you look at the women who have fractures, a lot don't have osteoporosis based on the DEXA [results]," Templeton says. Researchers speculate that in these cases bone architecture may be the problem -- but as yet, there is no realistic way to evaluate it.

Results also aren't as accurate if you are smaller or larger than average, Cosman says. So the test may underestimate your bone density if you are 5 feet tall or shorter, and may overestimate it if you are 5 feet 10 inches or taller.

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