Bone-Mineral Density Test

Why You Need It: To find out whether you're at risk for osteoporosis. This crippling weakness of the bones afflicts nearly 10 million older Americans, 80 percent of whom are women, according to the National Osteoporosis Foundation.

When and How Often: Have your first DXA (dual-energy X-ray) test at age 65 and another every five years thereafter. Women can lose up to 30 percent of their bone mass in the five to seven years following menopause. Get tested at menopause if you weigh less than 127 pounds, have ever smoked, have a history of nontraumatic fractures as an adult, or have a family history of osteoporosis.

What to Expect: The DXA test, the most accurate bone-density test, is safe and noninvasive: You lie fully clothed on a table while the X-ray machine scans your spine, hips, and wrists. If your bone density is low, your doctor may recommend the NTX test, a urine test that measures the rate at which you're losing bone mass; she may also want you to be X-rayed annually.

What the Results Mean: If your DXA shows you have osteopenia, a preosteoporotic state of low bone density, your doctor will recommend you consume at least 1,000 milligrams of calcium and 400 to 800 IUs of vitamin D daily without fail. (All women should get this amount, in fact.) She'll also suggest regular exercise. If you have osteoporosis, your doctor may give you a drug like Actonel or Fosamax.