Q: My mom's OB/GYN recommended she get a DEXA test, for measuring bone density. Is she at risk for osteoporosis?

A: From the sound of it, your OB/GYN is recommending this test to establish a baseline reference. Those test results will tell her how aggressive to be in helping you ward off osteoporosis, which affects half of all women over 50. Bone density, after all, peaks during your thirties. The higher your bone mineral density (BMD) during that period, the better your odds of keeping the inevitable loss of some bone density from changing the direction of your life. Fortunately, acting now also puts you in the right defensive position for the years ahead.

The DEXA test, for dual energy x-ray absorptiometry, is one of three most commonly used to measure BMD. (The others are single photon absorptiometry and quantitative computed tomography.) All three, which are noninvasive and painless, evaluate BMD at various sites--such as the spine, hip and other areas prone to fracture--or throughout the entire body.

The most commonly used of all, DEXA sends a very small amount of x-rays (for a spinal scan, it's about one-tenth of what's used in a chest x-ray) up from beneath you. Overall, the entire process may take as little time as five minutes, depending on which areas of the body are being scanned. You also do not necessarily need to undress, although buckles, zippers and large buttons may skew the results.

An overhead detector records how much radiation passes through you and relays this information to a computer. Your readings, along with data such as your age, sex, weight, and ethnic group, are then compared against a reference population. From the report generated, your physician can tell how you stand in comparison with the expected readings for women of your age, sex, and weight. (If possible, follow-up tests should be taken on the same machine and at the same facility.)

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The results of your DEXA of any other BMD scan will determine where you go from there. At the very least, the National Osteoporosis Foundation recommends regular exercise and both calcium and Vitamin D supplements; a product called Citrical Caplets+D from Mission Pharmacal, for example, includes both in one. Doctors typically recommend women take 1000mg of calcium daily--or up to 1500mg for post-menopausal women--but of course that's something to take up with your primary-care physician.

Another course of action, estrogen replacement therapy (ERT), is often prescribed for post-menopausal women. Estrogen, after all, is known to help the body absorb calcium; the decrease in estrogen production following menopause means less calcium for the body as well--hence the use of ERT. Using the results from your latest DEXA test, your doctor at that point can prescribe the lowest dosage necessary to prevent bone loss while averting ERT's side effects. These include headache, abdominal pain and nausea. A similar treatment, hormone replacement therapy, or HRT, involves the prescription of progestin, a hormone, along with the estrogen to avoid another possible risk of ERT alone: endometrial cancer.

You'll be reassured to know that new ways of slowing down osteoporosis, or at least stopping its progress, are coming out all the time. For post-menopausal women who cannot or choose not to take estrogen, a number of new medications are increasingly becoming available. At your age, you don't yet need to think hard about these options. Following your doctor's recommendations based on your DEXA test, such as keeping in shape, is the best preparation you can make.