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?

Medically Reviewed by Louise Chang, MD on December 26, 2010
5 min read

Health-conscious women who wouldn't dream of skipping their Pap test or mammogram appointments can be woefully ignorant about another type of vital health check -- the bone density test.

This quick and painless evaluation, often done for the first time after menopause, can help predict whether you'll sprint through your middle years and beyond, or shuffle along painfully due to thinning bones and fractures. More importantly, the test results can help your doctor decide if medication or lifestyle changes are needed now to rescue your "thinning" bones.

"Bone density tests turn out to be a good predictor of fracture risk," says Felicia Cosman, MD, clinical director of the National Osteoporosis Foundation in Washington, and a New York physician. Minimizing that risk is important, because the older you are, the more serious a fracture can be -- often resulting in lengthy hospitalization and long-term loss of your mobility.

And certain women are at higher risk of low bone mass, called osteoporosis, in which bones are likely to fracture. What increases your osteoporosis risk?

  • A family history of the disease
  • Having a small, thin frame
  • Certain medical conditions, such as rheumatoid arthritis
  • Taking certain medications, such as corticosteroids
  • Lifestyle factors: Alcohol use; getting little exercise; smoking; drinking cola; a diet low in calcium, phosphorus, and vitamin D.

Unfortunately, many women are unsure if -- and when -- they need a bone density test, if they're aware of the test at all.

Some of the confusion about the test is understandable because official recommendations and advice from physicians on when to first get tested isn't in perfect agreement.

For instance, the National Osteoporosis Foundation as well as the American Association of Clinical Endocrinologists recommends all women aged 65 and over , as well as women and men after age fifty who experience fractures, get a bone density test. They also suggest that younger women who have gone through menopause and have one or more risk factors (such as family history of spine fractures) get tested, too.

Despite those guidelines, many physicians say that all average, healthy women should get a bone density test when they enter menopause, says Laura Tosi, MD, director of the bone health program at Children's National Medical Center in Washington. That makes sense, she says, because bone loss tends to speed up in the years after menopause, so getting a baseline idea of where you stand as you enter menopause gives you something to compare later scans to.

And some women should get the test even earlier, Tosi says. For instance, a woman who is 40 or so and suffers a "fragility" fracture -- a bone break that occurs when you fall from a standing height (about 5.5 feet or less) -- should get a bone density test, Tosi says. That type of fracture, she reasons, doesn't occur to strong bones.

Women who have been on high-dose corticosteroid medications to treat autoimmune disease such as lupus, along with women who have thyroid disease, should consider a bone density test, too, Tosi says, because they are more likely than others to have lower bone density.

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.

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."

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.

Depending on the test results, your health care provider may suggest a number of actions, from starting medication that helps maintain or build bone, to urging you to exercise more and pay attention to your calcium and vitamin D intake.

The schedule for the repeat test depends on the results and opinions differ. "If there is well-preserved bone, my rule is to repeat every five years," Cosman says. "If it's in the medium range -- one to two years. If it's very low and you are on medication -- every year."

Researchers are working on a method to make the science of fracture prediction more precise, Cosman says. The new method would base the prediction on the bone density test and other information such as medical history and age.

The hope is to tell a woman what her predicted risk of fracture is within a specific time frame, for example: Your risk is 10% in the next 10 years. "It will help people put things in perspective," Cosman says.