Bone Mineral Density Test

Written by Brian Krans | Published on August 15, 2012
Medically Reviewed by Peter Rudd, MD

Overview

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 the elderly.

The test is also referred to as a 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.

Why a Bone Mineral Density Test Is Performed

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

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

  • all women over the age of 65
  • women over the age of 60 who are at high risk for osteoporosis
  • men over the age of 70
  • people taking glucocorticoid medications (those prescribed for autoimmune disorders) for two months or longer

Women have an increased risk for osteoporosis if they smoke or have:

  • chronic kidney disease
  • early menopause
  • an eating disorder
  • a family history of osteoporosis
  • a “fragility fracture” (a broken bone caused by regular activities)
  • regular alcohol consumption (three or more drinks per day)
  • rheumatoid arthritis
  • a significant loss of height (a sign of compression fractures in the spinal column)

How to Prepare for a Bone Mineral Density Test

The test requires little preparation. Tell your doctor if you are pregnant or believe you could be pregnant because X-ray radiation could harm your fetus.

For most bone scans, you don’t even need to change out of your clothes. However, avoid wearing clothing with buttons, snaps, or zippers because metal can interfere with obtaining the 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 he or she has 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 the 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 to see 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, radiation levels are very low, so experts agree that the risk of radiation exposure is far lower than the risk of not detecting osteoporosis before you have a bone fracture.

The New York State Department of Health reports that the level of radiation exposure from a bone density scan is the same amount you would experience on a flight from California to New York (NYSOPEP).

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 zero is considered ideal.

The NIH offers the following guidelines for bone density (NIH):

  • 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
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