A DEXA scan uses two low-energy X-ray beams to measure bone density, primarily at the hip and spine. It’s the standard test for diagnosing osteoporosis and assessing fracture risk, and it can also provide a detailed breakdown of your body composition, including fat, muscle, and bone mass. The scan is quick, painless, and exposes you to less radiation than almost any other imaging test.
How a DEXA Scan Works
DEXA stands for dual-energy X-ray absorptiometry. The scanner sends two X-ray beams at different energy levels through your body. Because bone, muscle, and fat each absorb these beams differently, the machine can distinguish between them and calculate how dense your bones are, or how much of your body is made up of each tissue type.
Most bone density scans focus on the hip and lower spine, since these are the areas most vulnerable to osteoporotic fractures. A smaller, portable version called a peripheral DEXA scan can measure density in your wrist, finger, or heel, but it’s less comprehensive and typically used as a preliminary screening tool.
Bone Density: What the Scores Mean
Your DEXA results come back as a T-score, which compares your bone density to that of a healthy 30-year-old adult at peak bone mass. The scale works like this:
- T-score of -1 or higher: Healthy bone density.
- T-score between -1 and -2.5: Osteopenia, a milder form of bone loss that raises your fracture risk but isn’t yet osteoporosis.
- T-score of -2.5 or lower: Likely osteoporosis.
Every full point drop in T-score roughly doubles your fracture risk, so the difference between -1 and -2.5 is significant. If you fall in the osteopenia range, your provider may recommend lifestyle changes, supplements, or a follow-up scan in a year or two to see whether your bone loss is progressing. A score at or below -2.5 typically leads to a conversation about medication.
Body Composition Analysis
DEXA scans aren’t only for bones. A whole-body scan can break down your tissue into three categories: bone mineral, lean mass (mostly muscle), and fat mass. This makes it one of the most precise tools available for understanding what your body is actually made of, far more accurate than a bathroom scale or handheld body fat monitor.
The scan can measure skeletal muscle mass and your muscle-to-height ratio, which helps identify sarcopenia (age-related muscle loss). It also quantifies visceral adipose tissue, the fat stored deep around your organs. Visceral fat is metabolically active and linked to higher risks of heart disease and type 2 diabetes. Unlike the fat you can pinch under your skin, visceral fat isn’t visible from the outside, so two people at the same weight can have very different amounts of it. A DEXA scan can also calculate your fat mass index, which measures total body fat relative to your height, independent of how much muscle you carry. Athletes, fitness enthusiasts, and people managing chronic conditions sometimes use body composition scans to track changes over time.
Who Should Get Screened
The U.S. Preventive Services Task Force recommends routine bone density screening for all women 65 and older. Postmenopausal women younger than 65 should be screened if they have risk factors for osteoporosis, including low body weight, a parent who fractured a hip, smoking, excess alcohol use, or long-term use of corticosteroids or insulin.
For men, there’s no universal screening recommendation yet because evidence on the benefits is still limited. That said, men share many of the same fracture risk factors: increasing age, low BMI, smoking, heavy drinking, steroid use, prior fractures, frequent falls, low testosterone, and diabetes. If several of those apply to you, it’s reasonable to ask about testing.
These screening guidelines apply to adults 40 and older who don’t already have a known diagnosis of osteoporosis or a history of fragility fractures. People with conditions that directly cause bone loss, such as hyperthyroidism, certain cancers, or metabolic bone diseases, follow a different testing schedule based on their specific situation.
What to Expect During the Scan
A central DEXA scan (hip and spine) takes about 10 to 30 minutes. You lie on your back on a padded table while a scanning arm passes over you. There’s no enclosed tube like an MRI, no noise, and no discomfort. You may be asked to keep your legs straight or rest them on a padded platform. A peripheral scan of your hand, wrist, or foot takes only a few minutes.
Preparation is minimal. You can eat normally on the day of the exam, but you should stop taking calcium supplements at least 24 hours beforehand, since undigested calcium in your system can skew the readings. Wear loose, comfortable clothing without metal zippers, buttons, or belts, and leave jewelry at home. You’ll also need to remove keys, wallets, or anything else in the scan area.
Radiation Exposure
A DEXA scan delivers about 0.001 millisieverts of radiation. For comparison, a standard chest X-ray delivers roughly 0.1 millisieverts, making a DEXA scan about 100 times lower in dose. You get more radiation exposure on a cross-country flight than from a bone density scan.
How Often You’ll Need One
Medicare covers a DEXA scan once every 24 months if you meet certain criteria: estrogen deficiency with osteoporosis risk, X-ray findings suggesting bone loss, use of steroid medications, a diagnosis of primary hyperparathyroidism, or monitoring to see whether osteoporosis treatment is working. More frequent scans can be covered if deemed medically necessary.
If your first scan shows healthy bone density, your provider may not recommend another one for several years. If you’re in the osteopenia range or starting treatment for osteoporosis, follow-up scans every one to two years help track whether your bone density is stable, improving, or continuing to decline. Using the same machine for repeat scans gives the most reliable comparison, since slight calibration differences between machines can affect your scores.