A bone density test determines if you have osteoporosis — a disease that causes bones to become more fragile and more likely to break.
A bone density test uses X-rays to measure how many grams of calcium and other bone minerals are packed into a segment of bone. The bones that are most commonly tested are in the spine, hip and forearm.
To accurately detect osteoporosis, doctors commonly use DEXA bone densitometry to measure bone mineral density (BMD). DEXA is a quick, painless procedure for measuring bone loss. Measurement of the lower spine and hips are most often done.
Peripheral dual-energy X-ray absorptiometry (P-DEXA) machine, which measures bone density in the wrist or forearm, are portable units that can be used in a doctor’s office.
DEXA bone densitometry is commonly used to diagnose osteoporosis, a condition that often affects women after menopause but may also be found in men. Osteoporosis involves a gradual loss of calcium, causing bones to thin, become more fragile, and more likely to break.
The DEXA test can also assess your risk for developing fractures and is effective in tracking the effects of treatment for osteoporosis and other conditions that can cause bone loss. Bone density testing is recommended for:
- post-menopausal women age 60 or older who have risk factors for developing osteoporosis
- patients with a personal or maternal history of hip fracture or smoking
- post-menopausal women who are tall (over 5 feet 7 inches) or thin (less than 125 pounds)
- men and women who have hyperparathyroidism
- men and women who have been medications that are know to cause bone loss for an extended period of time
- Refrain from taking calcium supplements for at least 24 hours beforehand.
- Wear comfortable clothing and avoid garments that have zippers, belts or buttons made of metal.
- Let your technologist know if you’ve recently had a barium examination or have been injected with a contrast material for a CT or radioisotope scan.
- Let your technologist know if there is a possibility you are pregnant.
Depending on the equipment used and the parts of the body being examined, the test takes between 10 and 30 minutes.
- You may be asked to undress and put on a gown.
- You’ll lie on a padded table with an x-ray generator below and a detector (an imaging device) above. It is important that you remain as still as possible during the procedure to ensure a clear and useful image.
- When evaluating bone loss in the spine and hip where most osteoporosis-related fractures happen:
- Spine: During an examination of the spine, your legs will be supported on a padded box to flatten your pelvis and lower (lumbar) spine.
- Hip: The technologist will place your foot in a brace that rotates the hip inward.
- The detector is scanned over the area, generating images on a computer monitor.
DEXA bone densitometry is a simple, painless, and non-invasive procedure. Once on the examination table, you may be asked to remain still and to hold an awkward position for a short period of time while the machine takes measurements.
Who interprets the results and how do I get them?
The results of a DEXA bone density exam are interpreted by a radiologist and forwarded to your doctor. Your test results will be in the form of two scores:
T score – This number shows the amount of bone you have compared to a young adult of the same gender with peak bone mass. A score above -1 is considered normal. A score between -1 and -2.5 is classified as osteopenia, the first stage of bone loss. A score below -2.5 is defined as osteoporosis. It is used to estimate your risk of developing a fracture.
Z score – This number reflects the amount of bone you have compared to other people in your age group and of the same size and gender. If it is unusually high or low, it may indicate a need for further medical tests.