Your physician may order a bone densitometry if he or she suspects you have or are in danger of developing osteoporosis. People with osteoporosis have weak bones or a significant loss of their bone mineral density. Millions of women and many men develop osteoporosis as they age.
The weakening of bones increases your risk of suffering broken bones. Bone densitometry is generally considered the best test to evaluate for the presence and severity of osteoporosis. It can enable you and your physician to devise a treatment plan to maximize your bone health.
How Bone Densitometry Works
Sometimes this exam is called bone density scanning or dual-energy x-ray absorptiometry (DXA). It’s an enhanced form of x-ray technology. The DXA machine sends a thin, invisible beam of low-dose x-rays through the bones. Your soft tissues absorb the first energy beam. Your bones absorb a second beam. By subtracting the soft tissue amount from the total, the machine provides a measurement of your bone mineral density (BMD). That density tells the physician the strength of your bones.
Why Physicians Use Bone Densitometry
Usually your physician uses bone densitometry (DXA) to diagnose osteoporosis. Osteoporosis involves a loss of calcium in your bones. It’s a condition that often affects women after menopause. Men can have osteoporosis, too. Along with the calcium loss, the bones go through structural changes that cause them to become thinner, more fragile, and more likely to break.
DXA also helps radiologists and other physicians track the effectiveness of treatments for any type of bone loss condition. The exam’s measurements give evidence about your risk of breaking a bone. You may have one of many other conditions that could motivate your physician to recommend this exam. Women discontinuing estrogen should be considered for bone density testing.
Why Physicians Use Vertebral Fracture Assessment (VFA)
Another exam performed on the DXA machine is vertebral fracture assessment (VFA). It’s a low-dose x-ray examination of the spine that assesses your backbone health. A VFA will reveal whether you have compression fractures in your vertebra (the bones in your spine). The presence of a vertebral fracture is of even more value in predicting your risk of bones breaking in the future than DXA alone.
Preparing for Your Bone Densitometry Exam
On your exam day:
- Eat normally, but don’t take calcium supplements for at least 24 hours before your exam.
- Wear loose, comfortable clothing. Avoid clothes with metal zippers, belts, or buttons.
- We may ask you to remove some or all of your clothes and to wear a gown during the exam. You may also have to remove jewelry, eye glasses, and any metal objects or clothing. Items like these can interfere with the x-ray images.
- Let your physician know if you recently had a barium examination or have been injected with a contrast material for a computed tomography (CT) scan or radioisotope (nuclear medicine) scan.
- Always inform your physician or our technologist if there is any possibility that you are pregnant.
What to Expect during the Exam:
- You will lie on a padded table. For a Central DXA exam, which measures bone density in the hip and spine, the x-ray generator is below you and an imaging device, or detector, is above.
- To assess your spine, your legs are supported on a padded box to flatten your pelvis and lower (lumbar) spine. The detector slowly passes over, generating images on a computer monitor.
- To assess the hip, a technologist will place your foot in a brace that rotates your hip inward. The detector slowly passes over, generating images on a computer monitor.
- You must hold very still.
- In certain instances, a forearm bone densitometry may be performed.
- The test usually takes 10 to 20 minutes, depending on the equipment used and the parts of the body being examined.
Benefits & Risks
Bone densitometry is simple, quick, and noninvasive. It doesn’t require any anesthesia. The amount of radiation used is very small—significantly less than the dose of a standard chest x-ray and the equivalent of a few days exposure to natural radiation.
With any x-ray procedure, there’s a very slight chance of cancer from exposure to radiation. However, the benefit of an accurate diagnosis far outweighs the risk. Women should always inform their physician or our technologist if there is any possibility of pregnancy.
Bone densitometry cannot predict with 100% certainty if you will experience a fracture in the future. However, it can provide strong indications of your risk of a future fracture.
Despite its effectiveness in measuring bone strength, bone densitometry or DXA is of limited use for people with a spinal deformity or for people who have had spinal surgery. If you have vertebral compression fractures or osteoarthritis, your condition may interfere with the test’s accuracy. In these instances, another test may be performed, such as a forearm bone densitometry.