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Measuring Bone Health

Page last modified on: July 31, 2008

At a Glance

DEXA scan basics

  • The DEXA scan evaluates bone mineral density, or BMD.
  • The results predict the likelihood of fracture.
  • BMD is generally measured in the spine and hip.
  • The DEXA scan calculates bone density based on the amount of radiation absorbed by the bone, and compares your bone strength with that of young premenopausal women and other women in your age group.
  • The diagnosis of osteoporosis means that your bone density has fallen below the range expected in premenopausal women (often called a T-score below -2.5).
  • The results are kept in your medical chart for comparison with future DEXA scans.
  • A single measurement tells the doctor how strong your bones are at the time of the measurement, but cannot tell if you have lost bone in the past, or if you will lose bone in the future.
  • If you have osteoporosis (a T-score below -2.5) your doctor may assume that you were in the normal range in your younger years, and that you have lost bone, There is no way of predicting whether your osteoporosis will get worse from this single measurement.
  • If your bone mass is in the lowest part of the young normal range (16%), your doctor may tell you that you have "osteopenia." This only means that you are at greater risk of getting osteoporosis in the future. If you are postmenopausal and have osteopenia, you are also at increased risk of fracture. But your risk of fracture would be higher if you had osteoporosis.

There are a number of tools that your doctor can use to check your bone health, including a physical exam and blood and urine tests to measure your calcium levels.

In general, your doctor may order a bone mineral density test if you're older than 45 and have had any of the following:

  • a broken bone
  • height loss
  • change in posture
  • back pain

Bone density tests use x-rays or sound waves to measure how strong your bones are. Bone density tests are used to definitively diagnose bone loss and osteoporosis.

dexa_scanThe most widely recognized bone mineral density test is dual-energy x-ray absorptiometry, commonly known as a DEXA scan. A DEXA scan uses low levels of x-rays and is quick and painless. A scanner passes over your whole body while you're lying on a cushioned table. A DEXA scan can measure the bone mineral density of your whole skeleton, as well as specific points that are more likely to break, such as the hip, spine and wrist. Using a DEXA scan to measure bone mineral density at the hip and spine is considered the most reliable way to diagnose osteoporosis and predict the risk of breaking a bone.

Your DEXA scan results are in the form of two scores:

  • T-score: Your T-score is the difference between your bone density and the average bone density of young, healthy woman. A score above -1 is considered normal. A score between -1 and -2.5 is classified as osteopenia and a score below -2.5 is classified as osteoporosis. Your T-score is used to estimate your risk of breaking a bone.
  • Z-score: Your Z-score is the amount of bone you have compared to other women of your age and race. If this score is very high or very low, you may need further tests.

Your doctor will help you interpret the results and understand what it means for your unique situation.

In general, doctors recommend that women 65 and older get a DEXA scan or other osteoporosis screening each year. But women may need to start screening earlier if they:

  • are underweight
  • smoke
  • have lost height or developed stooped or hunched posture
  • have sudden back pain with no apparent cause
  • are older than 45 and break a bone
  • have a chronic illness

No matter your age, if you've been diagnosed with breast cancer, your doctor will probably recommend a baseline DEXA scan before you start treatment and then regular DEXA scans as you move through treatment. This will allow you to make sure your bones are staying strong and take protective measures if you do start to lose some bone.

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