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What Do the Numbers Stand for in a Bone Scan Test?

Unless you get a bone scan, it is almost impossible to tell if you have adequate bone mass. You might have osteoporosis and not even know it. This is why it is called the "silent" disease according to Pamela Stuppy, R.D. and expert on osteoporosis. Understanding bone scan scores can provide you with valuable information and predict your risks for disease and fracture.

  1. Types of Bone Density Tests

    • Bone scans, bone density tests, and densitometry all measure bone mineral density (BMD) or bone mineral content (BMC) by using x-rays, gamma rays, or sound waves. You could get many kinds of scans: quantitative computed tomography (QCT), quantitative ultrasound (QUS), central DEXA (Dual energy x-ray absorptiometry), peripheral DEXA, and magnetic resonance imaging (MRI). DEXA bone scans are most common.

    Bone Mineral Content and Density Numbers

    • With DEXA testing, the total bone size and the density (mineral per square inch) is calculated. The size of the area tested will be indicated in centimeters (cm2). The bone mineral content will be shown in total grams (12.05 for example). And the bone mineral density will be a division of size and bone mineral content in decimal format, such as .736.

    T-Score

    • The t-score is about the thickness or density of the bone in comparison to an average, healthy, and young person of the same gender. This number compares your bone mass to that of someone who has achieved peak bone mass.

    Z-Score

    • The z-score is a measurement of a specific bone compared to the same bone in a similarly-aged, same-sexed person. It provides a reliable point of comparison and indicates the extent of the bone loss situation.

    Conclusions

    • Your t-score is used to diagnose osteoporosis (a t-score of -2.5 deviations from the standard norm). The more negative the score, the greater, the bone loss. On the other hand, z-scores show if you have excessive bone loss for your age. They also help determine what type of osteoporosis is present and how to treat it.

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