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Bone Mineral Density Test

What Is a Bone Mineral Density Test?

A bone mineral density test uses X-rays to measure the amount of minerals — namely calcium — in your bones. This test is important for people who are at risk for osteoporosis, especially women and older adults.

The test is also referred to as dual energy X-ray absorptiometry (DXA). It is an important test for osteoporosis, which is the most common type of bone disease. Osteoporosis causes your bone tissue to become thin and frail over time and leads to disabling fractures.

Why a Bone Mineral Density Test Is Performed

Your doctor may order a bone mineral density test if they suspect that your bones are becoming weaker, you are displaying symptoms of osteoporosis, or you have reached the age when preventive screening is necessary.

The National Institutes of Health (NIH) recommend that the following people get preventive screenings for bone mineral density:

  • all women over the age of 65
  • women under the age of 65 who have a high risk of fractures

Women have an increased risk for osteoporosis if they smoke or consume three or more alcoholic beverages per day. They are also at an increased risk if they have:

  • chronic kidney disease
  • early menopause
  • an eating disorder resulting in low body weight
  • a family history of osteoporosis
  • a "fragility fracture" (a broken bone caused by regular activities)
  • rheumatoid arthritis
  • significant height loss (a sign of compression fractures in the spinal column)
  • very inactive physically and do minimal weight bearing activities

How to Prepare for a Bone Mineral Density Test

The test requires little preparation. For most bone scans, you don’t even need to change out of your clothes. However, you should avoid wearing clothing with buttons, snaps, or zippers because metal can interfere with X-ray images.

How a Bone Mineral Density Test Is Performed

A bone mineral density test is painless and requires no medication. You simply lie on a bench or table while the test is performed.

The test may take place in your doctor’s office, if they have the right equipment. Otherwise, you may be sent to a specialized testing facility. Some pharmacies and health clinics also have portable scanning machines.

There are two types of bone density scans:

Central DXA

This scan involves lying on a table while an X-ray machine scans your hip, spine, and other bones of your torso.

Peripheral DXA

This scan examines the bones of your forearm, wrist, fingers, or heel. This scan is normally used as a screening tool to learn if you need a central DXA. The test takes only a few minutes.

Risks of a Bone Mineral Density Test

Because a bone mineral density test uses X-rays, there is a small risk associated with radiation exposure. However, the radiation levels are very low. Experts agree that the risk posed by this radiation exposure is far lower than the risk of not detecting osteoporosis before you get a bone fracture.

Tell your doctor if you are pregnant or believe you could be pregnant. X-ray radiation could harm your fetus.

After a Bone Mineral Density Test

Your doctor will review your test results. The results, referred to as a T-score, are based on the bone mineral density of a healthy 30-year-old compared to your own value. A score of 0 is considered ideal.

The NIH offers the following guidelines for bone density scores:

  • normal: between 1 and -1
  • low bone mass: -1 to -2.5
  • osteoporosis: -2.5 or lower
  • severe osteoporosis: -2.5 or lower with bone fractures

Your doctor will discuss your results with you. Depending on your results and the reason for the test, your doctor may want to do follow-up testing and come up with a treatment plan to tackle any issues.

Content licensed from:

Written by: Brian Krans
Medically reviewed on: Dec 22, 2015: William A Morrison MD

This feature is for informational purposes only and should not be used to replace the care and information received from your health care provider. Please consult a health care professional with any health concerns you may have.
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