Osteoporosis may be a silent thief, but there are now ways to sneak a peek at the insides of your bones to see what the bandit is up to.

In the past the best that doctors could do was take bone X-rays, which could detect bone loss only when it reached the dangerous 30 percent level.Now there is the DEXA (duel energy X-ray absorptiometer), which can measure bone loss as small as 1 percent. The DEXA cannot measure the rate at which you are losing bone, but two tests administered a year apart can give you a clue to rate of loss.

According to Hunter Heath III, chief of endocrinology, metabolism and diabetes at the University of Utah School of Medicine, the DEXA is more accurate and provides a lower dose of radiation than a CT scan and is more accurate than the newer ultrasound bone test.

Although the ultrasound is less expensive, requires no radiation and may be statistically accurate for large groups of women, "the predictive power of the test for you is poor."

Bone tests are recommended for women at high risk for osteoporosis - thin, white or Oriental women who have a family history of osteoporosis or who have other risk factors. The test is especially useful for high-risk women who need proof of bone deterioration to convince them to embark on estrogen therapy.

One of the risk factors that may warrant a bone test is long-term use of thyroid medication, although the thyroid/osteoporosis link is controversial.

"For every paper that says (thyroid medication) is bad there is another that says it isn't," says Heath.

Although researchers generally agree that too much thyroid hormone over a long period of time (either naturally occurring or through medication) can lead to fractures, it's not clear how much thyroid hormone is "too much."

Dr. Leonard Wartofsky, professor of medicine at the Uniformed Services University of the Health Sciences, suggests that doctors regularly monitor their thyroid patients for proper TSH levels and that doctors also encourage their thyroid patients to take adequate calcium and exercise, to consider taking estrogen and to avoid tobacco and excessive alcohol.

There are currently over 4 million women taking synthetic thyroid. Many of them, however, may not have visited a doctor or had a TSH test for years, even though the need for thyroid medication is known to decrease with age.