A BMD (bone mineral density) test is a type of imaging test that is used to measure the density (strength) of bones. Bone mineral density is used to estimate a person’s risk of having a fracture.
A BMD test is recommended in the following situations:
- Women over age 65 and men over age 70
- Women under age 65 and men age 50-70 who have risk factors for fracture including:
- A previous fracture caused by normal activities, such as a fall from standing height or less (this is called a “fragility fracture”)
- A chronic disease such as Rheumatoid Arthritis or kidney disease
- Women who undergo menopause before age 45
- History of hormone treatment for prostate or breast cancer
- Significant weight loss
- Strong family history of osteoporosis (e.g. parent suffered a hip fracture)
- Taking prednisone every day for more than 3 months
- Three or more units of alcohol per day on most days
The result of this test is reported as a “T-score.” The T-score is a measure of a person’s bone strength compared to that of a young, healthy adult. T-scores fall into 3 ranges:
- -1 to 0 indicates normal bone density
- -1 to -2.5 indicates reduced bone density (also called “osteopenia”)
- -2.5 and lower indicates low bone density (also called “osteoporosis”)
The BMD test typically measures bone density in two areas: the hip and the lower back. The BMD test is very simple and painless. It usually takes about 10-20 minutes. During a BMD test, a person lies flat on a table and a special X-ray machine passes over the body.
The test is usually repeated every 1-3 years depending on a person’s risk of fracture. For example, a person with normal bone density and no other risk factors for fracture might have a BMD repeated after 3 years, whereas a person with low bone density and multiple risk factors for fracture might have a BMD repeated every year. If a BMD test is repeated, it must be done on the same machine every time. Each machine is a little different so the same one needs to be used to accurately identify changes in BMD over time.
The BMD test results are important to consider because:
- It gives an estimate of a person’s risk of fracture
- It can help monitor response to treatment in those being treated for osteoporosis