Bone Density (DXA) Scan
Having a baseline understanding of your fracture risk is a key first step in improving your bone health. A bone density (DXA) scan is the test that measures the health of your bones.
Who should have a bone density (DXA) scan?
Consult with your physician if you think you might have risk factors for osteoporosis. Many physicians recommend screening for:
- All women aged 65 and older.
- All men aged 70 and older.
- Anyone with a fragility fracture (low trauma broken bone; such as a simple fall, bumping into something or coughing).
- Anyone with a disease, condition or medication associated with osteoporosis.
- Anyone who is considering therapy for osteoporosis, if bone density testing would facilitate the decision.
- Women who have been on hormone replacement therapy for prolonged periods.
- Anyone being treated for osteoporosis, to monitor the effects of therapy.
What is a Bone Density Scan?
A bone density scan, also called Dual Energy X-ray Absorptiometry (DXA) or bone densitometry, is the most accurate method of measuring your bone mineral density, diagnosing osteoporosis and assessing your risk of fractures.
How does a DXA scan work?
A bone density scan is painless, safe, does not involve anesthesia, injections, contrast materials, needles, enemas, or medications. The DXA machine emits a narrow beam of very low doses of X-ray (less than radiation from an airplane trip and equivalent to two hours of direct sunshine) to rapidly scan and measure the density of your bones. DXA is most often performed on the lower spine and hips and forearms. A computer converts the information to numbers indicating your bone density. There are no aftereffects.
What should I expect during my bone density scan appointment?
You will fill out a questionnaire to help the doctor determine your risk for osteoporosis. The technologist will measure your height and weight.
During the scan you will lie on your back on a comfortable, padded table for several minutes. The scan will examine the lower spine, both hips and other important points on your skeleton. To assess the spine, your legs will be supported on a pad to flatten the pelvis and lower spine. To assess the hip, your foot will be positioned in a way that rotates the hip inward. A scanner arm above you will slowly pass over the part of your body being examined, generating images on a computer monitor.
The machine will not touch your body. You will need to remain as still as possible for the scan. The bone density scan takes about 20 minutes. You can resume your usual activities immediately afterwards.
What information does a DXA scan provide?
For each bone tested, DXA provides two scores by comparing your bone density with data in a large, validated database:
- Z-score: The number of standard deviations above or below the mean value for age-, gender-, and ethnicity-matched people.
- T-score: The number of standard deviations above or below the mean value for young normal adults of the same gender.
T-score is used to categorize or rate bone density:
- A normal T-score is -1.0 or greater.
- A T-score between -1.0 and -2.5 indicates low bone density.
- A T-score of less than -2.5 shows osteoporosis.
What does it mean to have “low bone density” but not osteoporosis?
Low bone density suggests some increased risk for fragility fracture. Your risk can be estimated from your age, gender, ethnicity, history and other individual risk factors. Your risk of having a hip fracture or other major broken bone in the next 10 years is used to determine whether you should consider prescription treatment for bone fragility.
How should I prepare for a bone density scan?
- On the day of the exam you may eat normally. You should NOT take calcium supplements for at least 24 hours before your exam.
- Wear loose, comfortable clothing. Avoid garments that have zippers, belts or buttons made of metal. Remove objects such as keys or wallets that would be in the area being scanned.
- You may also need to remove jewelry and any metal objects or clothing that might interfere with the X-ray images.
- Let us know if you:
- Recently had a barium examination or nuclear medicine scan. You may have to wait 10 to 14 days before undergoing a bone density test.
- Are pregnant or think you may be pregnant.
- Have any metal in your body, such as spinal fusion rods or a hip replacement.
- Have a severely curved spine, prior spinal surgery or have difficulty lying on your back.
- If you have test results from any prior bone density scans, please bring them to your appointment.