DXA - A Window Into Your Bone Density

By Dr. Adam Perlman

We don’t usually think about – or even notice – our bones until there’s a problem, like a fracture. In the past, that’s how people would find out that they had bone loss – because their bones broke. Now, we have a reliable way to measure bone strength before a bone breaks.

Bone density, also called bone mineral density (or BMD), measures the mineral content of your bones. Higher mineral content means stronger bones. Lower mineral content can indicate a wide range of problems and higher risk of painful fractures. And because low bone density can cause such serious issues, it’s important to know where your bones stand.

Luckily, there’s a very simple way to find out: a DXA test.

DXA (sometimes referred to as DEXA) stands for dual-energy x-ray absorptiometry, and it measures your bone density. By using special x-ray technology (a particularly low radiation dose), this test actually measures how many grams of minerals – including calcium – are packed into a section of bone.

That valuable information tells you and your doctor:

• whether your bone density is decreasing
• your fracture risk
• if you have osteoporosis or osteopenia
• whether your bone-strengthening treatment is working

Now, a DXA scan typically looks at bone only in one part of your body. Which bone they look at depends on a couple of factors, including the type of machine being used for the test. Portable machines, like the kind you’ll see in a pharmacy or at a health expo, are used to measure bone density in the smaller bones at the ends of your limbs: heels, fingers, and wrists. Central devices, the kind they have in hospitals, usually take measures of your lower spine (officially called your lumbar vertebrae), the top of your thighbone (femur), or the bones in your forearm.

Since your bone density may not be the same in different parts of your body, a test in one area (like your heel) can’t accurately predict the bone density in another area (such as your spine). That’s why your doctor may recommend a follow-up test if a portable device shows low bone density.

When should I get tested?

Since bone loss is associated with aging, the guidelines for getting tested start with age. According to the American Academy of Family Physicians (AAFP), the time to get tested is at age 65 for women, and at age 70 for men… but that’s if you have no known risk factors.

There are certain factors that make you a good candidate for the test, no matter how old you are.

• Long-term course of steroid medication (like prednisone), which slows down the natural bone-building process
• A drop in sex hormone (like estrogen and testosterone) levels, brought on by menopause and many cancer treatments
• Lost height (1.6” or more) can indicate spinal compression fractures, often caused by osteoporosis
• “Fragility” fractures, which happen when bones break unexpectedly, like because you sneezed, bumped into furniture, or fell from a very low height (which wouldn’t normally cause a break)
• Certain chronic diseases, including rheumatoid arthritis and chronic kidney disease
• Use of thyroid hormone replacement medication

Once you’ve had your first scan, the general recommendation is to follow up every two years. Based on your unique situation and your current test scores, you may need a repeat scan more or less frequently.

Know Your Scores

Once you’ve had a DXA scan, your results get reported as two numbers, the T-score and the Z-score. Both of these scores are measured in units called standard deviations that show how close your BMD is to the average.

Your T-score measures your BMD compared to the BMD of a young, healthy person of your sex. This score can tell you where your bone density falls on the path to osteoporosis, and helps predict your fracture risk. Here’s what the numbers mean:

Your Z-score shows how your BMD compares to other people of your age, gender, weight, and race. This score helps you find out if your bone loss may be caused by factors other than age. If your Z-score was -2.0 or lower, that indicates something other than normal aging is leading to abnormal bone loss. Once you and your doctor figure out what the underlying problem is (such as long-term use of certain medications), you can take steps to limit, stop, and reverse that bone loss.

What can you do?

Even with very low DXA scores, there’s a lot you can do to slow down – and even reverse – bone loss. For one thing, you can increase the number of bone-healthy foods in your diet. Special exercise programs can help you rebuild solid bones. Plus, there are dietary supplements that can help enhance your body’s natural bone-building capabilities. And even if your numbers are looking good for now, preventing bone loss is better than trying to reverse it… so start beefing up your bones today.