A DEXA scan (also written as DXA) is an imaging test that uses two low-energy X-ray beams to measure bone density and body composition. It’s the gold standard for diagnosing osteoporosis and assessing fracture risk, and it takes about 15 to 20 minutes. The name stands for Dual-Energy X-ray Absorptiometry.
How a DEXA Scan Works
The scan passes two X-ray beams at different energy levels through your body. Bone tissue absorbs the higher-energy beam, while soft tissue lets more of the signal pass through. By comparing the two signals, the machine can precisely separate bone from everything else and calculate how dense your bones are at specific sites, typically the spine and hip.
This same two-beam technology also distinguishes fat tissue from lean tissue (muscle, organs, water), which is why DEXA scans have become popular for detailed body composition analysis beyond just bone health.
What the Scan Measures
A standard bone density DEXA focuses on the spine and the top of the femur (hip), the two areas most vulnerable to osteoporotic fractures. Some scans also measure the forearm. The machine produces a mineral density value for each site, which gets translated into scores you can compare against healthy reference populations.
A full-body composition DEXA goes further. It breaks your entire body down into three components: bone, fat, and lean mass. The report typically includes your total body fat percentage, a region-by-region breakdown of fat and muscle in your arms, legs, and trunk, and a measurement of visceral adipose tissue, the metabolically active fat surrounding your internal organs. It also calculates ratios like lean mass relative to height, which helps identify low muscle mass even in people whose overall weight looks normal.
Understanding Your T-Score
Bone density results come as a T-score, which compares your bone density to that of a healthy 30-year-old at peak bone mass. The thresholds are straightforward:
- T-score of -1 or higher: healthy bone density
- T-score between -1 and -2.5: osteopenia, a milder form of bone loss that signals your bones are thinning but haven’t reached the osteoporosis threshold
- T-score of -2.5 or lower: osteoporosis
These numbers matter because each full point drop in T-score roughly doubles your fracture risk. A score of -2.5 doesn’t mean your bones will break, but it puts you in a category where preventive treatment can make a real difference.
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 also be screened if they have risk factors for fractures, such as a family history of osteoporosis, low body weight, smoking, or long-term steroid use. For men, there isn’t enough evidence yet for a blanket screening recommendation, though individual doctors may order scans based on personal risk factors.
Medicare covers a bone density scan once every 24 months for eligible patients, or more frequently if there’s a medical reason. Private insurance policies vary, but most follow similar intervals for people with diagnosed bone loss or established risk factors.
What to Expect During the Scan
A DEXA scan is painless and noninvasive. You lie flat on a padded table while a scanning arm passes over you. There are no injections, no enclosed spaces, and no need to hold your breath. The whole process takes 15 to 20 minutes.
You’ll want to avoid wearing clothing with metal buckles, buttons, or zippers, since metal interferes with the X-ray readings. Most facilities will offer you a gown if needed. The one preparation step to remember: stop taking calcium supplements or multivitamins containing calcium at least 24 hours before the test. Calcium in your digestive tract can show up on the scan and skew results.
Radiation Exposure
DEXA scans deliver an extremely low radiation dose. A spine-plus-hip scan exposes you to roughly 1 to 15 microsieverts, depending on the type of machine. For context, you absorb about 10 microsieverts from natural background radiation on an ordinary day. Newer pencil-beam scanners deliver less than 1 microsievert, making them among the lowest-dose imaging tests in medicine.
Accuracy and Limitations
DEXA is highly reliable for tracking bone density over time, which is one reason it remains the diagnostic standard. But certain conditions can produce misleading results. Spinal arthritis, for instance, can cause bone density at the spine to read falsely normal because arthritic bone changes add extra mineral that the scan picks up as “dense” bone. Previous compression fractures can create similar artifacts.
When a standard DEXA doesn’t tell the whole story, some facilities use an add-on technology called trabecular bone score, which analyzes the internal texture of bone rather than just its density. This can reveal weakened bone structure even when the T-score looks normal, particularly in people who have already had a fracture. If your results seem inconsistent with your fracture history or risk profile, your provider may recommend hip-site measurements (which aren’t affected by spinal arthritis) or additional testing to get a clearer picture.
Bone Density vs. Body Composition Scans
It’s worth noting that the same DEXA technology serves two distinct purposes that attract very different audiences. Clinical bone density scans are medical tests ordered to screen for osteoporosis and guide treatment decisions. Body composition scans, increasingly offered at fitness clinics and sports medicine centers, use the same machine but focus on fat distribution, muscle symmetry, and visceral fat levels. These are popular among athletes and people tracking fitness progress because DEXA provides more precise body fat measurements than skinfold calipers or bioelectrical impedance scales.
A body composition scan also reports whole-body bone density as part of its standard output, so you get bone health data even when the primary goal is tracking muscle and fat. The report typically runs several pages and includes annotated images showing exactly where fat and lean tissue are distributed across your body.