Bone Mineral Density Test

What is a Bone Mineral Density Test?

A bone mineral density (BMD) test is a non-invasive and painless method to determine your bone health. A BMD test measures your bone minerals (calcium) and bone density to identify osteoporosis, determine your risk for fractures, and monitor your response to osteoporosis treatment.

A BMD test typically measures bone density in the spine, wrist, hip or total body. These are the most common areas of fracture as a result of osteoporosis, a disorder in which bones gradually become fragile and more susceptible to fractures.

A bone mineral density test using DEXA (dual energy X-ray absorptiometry) involves minor exposure to radiation. The amount of radiation exposure is less than that received during a chest X-ray.

There are several types of equipment and methods available to measure bone density. The most widely used is called a DEXA (dual energy X-ray absorptiometry), which measures the spine, hip or total body.

For this exam you will be asked to remove any clothing with zippers or other metal parts. You will lie comfortably on a padded examination table. The technologist will record your height and weight and may ask you some additional questions.

Then, you simply lie still while the equipment passes overhead. The entire scan takes a very short amount of time and is completely pain-free.

What Do the Results Mean?

Your bone density will be compared to two standards commonly referred to as age-matched, often called your Z-score, and young normal, often called your T-score. The age-matched standard compares your bone density to what is expected for someone your age, gender, ethnicity and size. The young normal standard compares your bone density to the ideal bone density of a healthy 30-year old adult of your same sex and ethnicity.

Normal - Bone density is within 1 standard deviation (+1 or -1) of the young adult average.

Low Bone Mass - Bone density is 1 to 2.5 standard deviations below (-1 to -2.5) the young adult average.

Osteoporosis - Bone density is 2.5 or more standard deviations below (-2.5 or less) the young adult average.

Using this information, your doctor will determine whether you are at risk for a fracture and can advise you on how to best maintain or improve your bone density. 

Risk Factors for Osteoporosis

You are at risk for osteoporosis if you:

  • Have a family history of osteoporosis (relatives with stooped posture or broken bones)
  • Are of Caucasian or Asian heritage
  • Are past menopause
  • Have a small or thin body structure
  • Have a diet low in calcium
  • Don't do weight-bearing exercise regularly
  • Smoke
  • Consume alcohol excessively
  • Have taken oral steroids, thyroid medication or anticonvulsants for a long time

The more you answered "yes," the higher your risk of osteoporosis

How Should I Prepare for the Test?

  • Wear comfortable clothing with no metal zippers, buttons or buckles.
  • You will be asked to remove any jewelry or metal items before the exam.
  • Inform the technologist if you have any metal implants inside your body, had any recent fractures, a recent nuclear medicine scan or a barium enema.


Always inform your doctor and the technologist if you are pregnant or think there is a possibility you may be pregnant.

(This information is intended to serve as a simple guide. It can never replace the conversations with your own doctor. It is not a substitute for professional care.)

(Some information on this page was provided courtesy of The St. John Companies, Inc. PO Box 800460 Santa Clarita, CA 91380)