DEXA (Dual-Energy X-Ray Absorptiometry)
DEXA Bone densitometry, also called dual-energy x-ray absorptiometry, DEXA or DXA, uses a very small dose of ionizing radiation to produce pictures of the inside of the body (usually the lower (or lumbar) spine and hips) to measure bone loss. It is commonly used to diagnose osteoporosis, to assess an individual’s risk OF developing osteoporotic fractures. DXA is simple, quick and non invasive. It’s also the most commonly used and the most standard method for diagnosing osteoporosis.
This exam requires little to no special preparation. You should not take calcium supplements for at least 24 hours before your exam.
Bone density scanning (DXA) or bone densitometry is an enhanced form of x-ray technology that is used to measure bone loss. DXA is today’s established standard for measuring bone mineral density (BMD).
An x-ray exam helps doctors diagnose and treat medical conditions. X-rays are the oldest and most often used form of medical imaging.
DXA is most often performed on the lower spine and hips. In children and some adults, the whole body is sometimes scanned. Peripheral devices that use x-ray or ultrasound are sometimes used to screen for low bone mass, mostly at the forearm. In some communities, a CT scan with special software can also be used to diagnose or monitor low bone mass (QCT). This is accurate but less commonly used than DXA scanning
DXA scans are also interpreted by other physicians such as rheumatologists and endocrinologists. A clinician should review your DXA scan while assessing the presence of clinical risk factors such as:
- Rheumatoid arthritis
- chronic renal and liver disease
- respiratory disease
- inflammatory bowel disease
Your test results will be in the form of two scores:
T score — This number shows the amount of bone you have compared with a young adult of the same gender with peak bone mass. A score of -1 and above is considered normal. A score between -1.1 and -2.4 is classified as osteopenia (low bone mass). A score of -2.5 and below is defined as osteoporosis. The T score is used to estimate your risk of developing a fracture and also to determine if treatment is required.
Z score — This number reflects the amount of bone you have compared with other people in your age group and of the same size and gender. If this score is unusually high or low, it may indicate a need for further medical tests.
Small changes may normally be observed between scans due to differences in positioning and usually are not significant.
- DXA bone densitometry is a simple, quick and non-invasive procedure.
- No anesthesia is required.
- The amount of radiation used is extremely small—less than one-tenth the dose of a standard chest x-ray, and less than a day’s exposure to natural radiation.
- No radiation stays in your body after an x-ray exam.
- X-rays usually have no side effects in the typical diagnostic range for this exam.
What are the limitations of Bone Densitometry (DEXA, DXA)?
- A DXA test cannot predict who will experience a fracture but can provide a relative risk and it is used to determine whether treatment is required.
- Despite its effectiveness as a method of measuring bone density, DXA is of limited use in people with a spinal deformity or those who have had previous spinal surgery. The presence of vertebral compression fractures or osteoarthritis may interfere with the accuracy of the test; in such instances, CT scans may be more useful.
- Central DXA devices are more sensitive and better standardized than pDXA devices but they are also somewhat more expensive.
- A test done on a peripheral location, such as the heel or wrist, may help predict the risk of fracture in the spine or hip. These tests are not as helpful in following response to treatment, however, and if they indicate that drug therapy is needed, a baseline central DXA scan should be obtained.
- Follow-up DXA exams should be performed at the same institution and ideally with the same machine. Bone density measurements obtained with different DXA equipment cannot be directly compared.