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Understanding DEXA Scan Results

written by: Diana Cooper•edited by: Leigh A. Zaykoski•updated: 2/19/2010

Find help with understanding DEXA scan results. Learn how the machine measures bone mineral density and know how the scores work.

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    Bone Loss

    Understanding DEXA scan results can be a bit confusing. Basically, the test will tell you how much bone loss has occurred. This information will determine if you have osteoporosis and give an estimate on what your chances are of breaking a bone.

    After the age of 40, bone mass (particularly calcium) begins to decline in both men and women, about 2% loss per year. As bone loss occurs, the bones become fragile (the bone mineral density, BMD, is low). The thinner they get, the more easily they can break.

    Osteopenia is a medical condition when BMD is lower than normal, but not low enough to be osteoporosis (although it is considered by some to be a precursor to osteoporosis).

    Osteoporosis is a disease in which the bones become very porous and are subject to fracture. Osteoporosis is uncommon in men, mainly because their bone mass is greater than women before the age of 40 and they do not go through menopause. If a male has osteoporosis, it is most likely due to an underlying condition such as long-term use of corticosteroids or hyperparathyroidism.

    Postmenopausal osteoporosis is the most common type and although the whole skeleton may be involved, bone loss is normally greatest in the ribs, spine, and hips.

    A DEXA scan (low-dose radiation x-ray) is the best device to use when measuring BMD because it provides the most accurate results, even with minimal loss (unlike a regular x-ray).

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    Understanding DEXA Scan Results

    The DEXA machine sends two distinct beams through the bone. One is absorbed by soft tissue and the other by bone. Subtracting the amount absorbed in the soft tissue from the total amount (soft tissue and bone) will equal the BMD.

    Results will have two types of scores:

    T Score

    This number compares the amount of bone you have to a young adult of the same sex with peak bone mass.

    The T score is used to define osteoporosis:

    • T -1 (T minus 1) or higher is normal
    • T -2.5 to -1 is considered osteopenia
    • T -2.5 and below is a diagnosis of osteoporosis

    The T score is used to make an estimate on your risk of having a fracture:

    • T 0 means your risk is the same as a normal 40 year old
    • T -1 means your risk is twice as likely
    • T -2 means your risk is four times as likely
    • T -3 means your risk is eight times as likely

    Z Score

    This number compares the amount of bone you have to a person in your age group of the same sex and size. If the Z score is unusually low or high, further medical tests may be needed.

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    Abnormal Results

    Having a low score does not necessarily mean you will have a fracture. There are other factors that influence the likelihood of breaking a bone, including age and medical conditions that can make one prone to falling.

    Your health care provider will work with you on an appropriate plan of care and will monitor your progress. Normally, a DEXA scan will be repeated in two years. For a more accurate comparison of results, it is best to have the test done using the same machine.

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    Sources Used