A simple guide to bone density testing

Further proof that aging isn't fair:  you can drink fat-free milk every day, pop calcium pills religiously, get plenty of weight-bearing exercise — and still develop osteoporosis.

Medication can slow this disease, which increases the risk of potentially devastating hip fractures and other broken bones. That makes early detection through bone density testing crucial.

• All women should begin having bone density tests by age 65. But some women should start earlier.
• Prime candidates for earlier testing include women who have reached menopause and have one or more risk factors, such as a family history of osteoporosis or a fractured bone.
• Doctors also use bone density tests to track how well a patient responds to treatments for osteoporosis and other bone disorders.
• There are no established testing guidelines for men, nor are there hard rules about how often anyone should have their bones tested.
• Women who are several years past menopause may lose only about one percent of bone mineral density per year.
• Such a small change would not be detected, so experts agree that waiting at least two years between exams is probably adequate.

Dual-energy X-ray absorptiometry (DXA, or DEXA for short) is the gold standard. DXA uses a low-dose X-ray to scan the hips and spine. The procedure is painless and takes about 15 minutes.

• All bone density tests produce a T score, which reflects the sturdiness of your skeleton compared to that of a healthy young adult.
• A T score between -1 and -2.5 means you have osteopenia, or low bone mass.
• A score of -2.5 or lower means you have osteoporosis.
• Each drop of 1 in your T score indicates that you are two to 2.5 times more likely than a healthy young adult to fracture a hip. It also means that your risk of all other bone fractures is increased 1.5 to two times.
• Keep in mind that fragile bones are just one cause of hip fractures and other broken bones, so having a stellar result on a DXA test or any other bone exam won't necessarily keep you out of a cast.
• In a study of more than 8,000 post-menopausal women, more than half the participants who suffered broken hips had received a normal DXA test result within the previous five years.
• Doctors will soon start using a new scoring system created by the World Health Organization that uses bone density and other factors — such as patient's age and whether she engages in activities such as walking or jogging, which protect against osteoporosis — to determine who's at risk for broken bones.
• Is a heel ultrasound as good as DXA? Many small hospitals and clinics don't offer DXA because they don't have the large, expensive machines.
• The most common alternative is heel ultrasound, which uses a small portable device to measure bone density in the heel.
• Heel ultrasound assumes that bone density in the foot is a good indicator of a person's overall risk of bone fracture. However, studies show that heel ultrasound misses osteoporosis in the hip about 30 percent of the time.
• Other alternatives to DXA include pDXA, which measures bone density in the finger, wrist or other "peripheral" site. Like heel ultrasound, pDXA is not as accurate as DXA but is a reasonable alternative if DXA is not available.
• However, if one of these tests produces a low T score indicating that you may have osteopenia or osteoporosis, seek out a DXA test to confirm the diagnosis.