Quick answer: a DEXA (or DXA) scan measures bone mineral density, usually in the lower spine and hips, to diagnose osteoporosis and estimate your risk of breaking a bone. It is quick (usually 10 to 30 minutes), painless and uses a tiny dose of radiation, less than a day of natural background radiation. Your result is given as a T-score: -1 and above is normal, between -1 and -2.5 is low bone mass (osteopenia), and -2.5 or below is osteoporosis. The USPSTF recommends screening for all women 65 and older, and for younger postmenopausal women at increased risk. Medicare covers it once every 24 months for people who qualify.
A DEXA scan is one of the easiest tests in imaging: you lie on a padded table while an arm passes slowly over you. The most important thing is what the numbers mean, so most of this guide focuses on that.
What does a DEXA scan measure?
DEXA stands for dual-energy x-ray absorptiometry. The machine sends a thin, low-dose x-ray beam with two energy levels through the bones being measured. One is absorbed mainly by soft tissue and the other mainly by bone; subtracting the soft tissue leaves your bone mineral density (BMD).
It is the standard test to:
- diagnose osteoporosis, a gradual loss of bone that makes bones thinner and more likely to break
- estimate your risk of fracture, together with other factors such as age, weight, previous fractures, family history, smoking and alcohol
- monitor treatment for osteoporosis and other conditions that cause bone loss
It is not the same as a bone scan, a nuclear medicine test that shows bone activity. See [link: Bone Scan: Preparation, Procedure and Results Timeline].
Who should have a DEXA scan?
In January 2025, the U.S. Preventive Services Task Force (USPSTF) recommended osteoporosis screening for:
- all women aged 65 and older
- postmenopausal women younger than 65 who are at increased risk of an osteoporotic fracture, based on a clinical risk assessment
For men, the USPSTF found the evidence insufficient to recommend for or against routine screening, so the decision is left to clinical judgment.
Your doctor may also recommend a DEXA scan if you, for example:
- had a fracture after only a minor fall or injury
- take medications that cause bone loss, such as long-term corticosteroids (prednisone), some anti-seizure drugs or high-dose thyroid replacement
- have conditions linked to bone loss, such as rheumatoid arthritis, chronic kidney or liver disease, type 1 diabetes, hyperthyroidism or hyperparathyroidism
- have an x-ray showing a possible spine fracture or signs of osteoporosis
- have a family history of osteoporosis or hip fracture
How to prepare
- Eat normally on the day of the test.
- Do not take calcium supplements for at least 24 hours before the scan.
- Wear loose clothes without metal: no zippers, belts or metal buttons around the hips and waist. You may change into a gown.
- Remove jewelry, keys, wallets, glasses and removable dental work if they are near the area being scanned.
- Recent tests: tell your doctor if you recently had a barium exam or an injection of contrast for a CT or a nuclear medicine scan. You may need to wait 10 to 14 days before the DEXA.
- Pregnancy: always tell your doctor and the technologist if you might be pregnant.
What happens during the scan
- You lie on your back on a padded table. The x-ray source is below you and the detector, on a movable arm, is above you.
- For the spine, your legs rest on a padded box to flatten your lower back.
- For the hip, your foot is placed in a brace that rotates the hip slightly inward.
- The arm passes slowly over the area. You need to stay still and may be asked to hold your breath for a few seconds.
- Sometimes the forearm is measured too, or a vertebral fracture assessment (VFA) is added: a low-dose image of the spine to look for compression fractures, which adds only a few minutes.
The test is usually done in 10 to 30 minutes and is completely painless. You may also be asked to fill out a short questionnaire about your fracture risk factors.
From the scanner room: [TU EXPERIENCIA: errores frecuentes que afectan a la medición (cremalleras, suplementos de calcio, contraste reciente) y cómo colocas a pacientes con dolor o poca movilidad.]
Understanding your results
A radiologist or another physician trained in bone densitometry interprets the scan and sends a report to your doctor. You will see two scores:
T-score: compares your bone density with that of a healthy young adult of the same sex at peak bone mass. It is used to diagnose osteoporosis and estimate fracture risk.
| T-score | What it means |
|---|---|
| -1 and above | Normal bone density |
| Between -1.1 and -2.4 | Low bone mass (osteopenia) |
| -2.5 and below | Osteoporosis |
Z-score: compares your bone density with people of your own age, sex and size. A Z-score that is unusually low may mean something other than aging is causing bone loss, and your doctor may order further tests.
Your report may also include a 10-year fracture risk estimate (often calculated with a tool called FRAX), which combines your DEXA results with your risk factors. Your doctor uses all of this to decide whether you need treatment.
Small differences between scans can come from positioning and are usually not significant.
Limitations
- DEXA cannot predict exactly who will break a bone; it estimates relative risk.
- Arthritis, spinal deformities, previous spine surgery or compression fractures can falsely raise spine readings. In such cases, the hip or forearm may be used, or a CT may be more useful.
- Follow-up scans should be done at the same place, ideally on the same machine, because results from different machines cannot be directly compared.
- Heel or wrist screening devices in pharmacies or health vans are less accurate; if they suggest a problem, a standard DEXA of the hip and spine is needed.
How often should you have a DEXA scan?
Changes in bone density happen slowly, so repeat scans are usually done about every two years. People on high-dose steroid medication may need follow-up sooner. Your doctor will set the interval.
Is it covered by insurance?
Medicare Part B covers a bone mass measurement once every 24 months (more often if medically necessary) if you meet at least one of these conditions:
- you are a woman whose doctor determines you are estrogen-deficient and at risk for osteoporosis
- your x-rays show possible osteoporosis, osteopenia or vertebral fractures
- you take, or are about to start, prednisone or other steroid-type drugs
- you have been diagnosed with primary hyperparathyroidism
- you are being monitored to see if your osteoporosis treatment is working
You pay nothing if your provider accepts Medicare assignment. Most private plans also cover screening that follows USPSTF recommendations; check with your plan. See [link: Does Medicare Cover MRI and PET Scans?].
Tips from the technologist
[TU EXPERIENCIA: 2-3 consejos propios. Ideas: ropa deportiva sin metal, hacer los controles siempre en el mismo centro, llevar los informes de densitometrías anteriores.]
Frequently asked questions
Is a DEXA scan safe?
Yes. It uses an extremely small radiation dose, less than one-tenth of a chest x-ray and less than a day of natural background radiation.
What is a normal T-score?
-1 or higher. Between -1 and -2.5 is osteopenia, and -2.5 or lower is osteoporosis.
Can I take calcium before a DEXA scan?
No. Stop calcium supplements for at least 24 hours before the test.
Do men need a DEXA scan?
Not routinely, according to the USPSTF, but your doctor may recommend one if you have risk factors such as long-term steroid use or a fracture after a minor fall.
Does a DEXA scan hurt?
No. You simply lie still on a padded table for a few minutes.
This article is for general information and does not replace advice from your doctor.