Osteoporosis and BMD Testing

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Category: Metabolic Bone Disease Published on Wednesday, 25 June 2008 Written by Yong Tsai, MD
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Like an aging tree whose trunk becomes dry and brittle, the density of our bones also decreases in time, setting us up for a possible bone fracture.

Our bones cells called osteoclasts break down bone creating tiny decay pits exceeds the formation of new bone called osteoblasts, thus leaving the bone weaker and less dense. As babies grow and mature, so do our bones. However, at around age twenty, we experience peak bone mass, which stabilizes until menopause for women and about ten years later for men. At this point, bone absorption surpasses its formation, causing osteoporosis.

Thanks to technical advances, diagnosing osteoporosis has become a quick, easy, painless, and very accurate process with the help of a Dual Energy X-ray Absorptiometry (DEXA-bone density testing). As you lie on the table, the bone density machine “arm” slides over you, measuring the size of your femur and vertebrae and calculates the amount of mineral in each square centimeter of bone. The average of three vertebrae (L2 to L4) and a total femur are then used to determine total bone density. Finally, more comparisons are made to calculate further measurements.

The best measurement you can use to predict a risk of fracture is the famous T-score or Young Adult Comparison, which is measured in standard deviations (SD) using a baseline comparison of the average 20-45 year old of T-score of 0.

Basically, BMD T-scores are divided into two levels: -1.0 to –2.49 showing osteopenia, and greater than –2.5 showing osteoporosis. For example, a T-score of –2.8 or 72% suggests that the patient has lost 28% of her peak bone density and that she has osteoporosis.

Fortunately, fractures can be minimized or prevented by following the guidelines of The National Osteoporosis Foundation that recommends treating postmenopausal women, regardless of risk factors, with a T-score of –2.0, and those with a T-score of –1.5 with previous fracture, weighing less than 127lbs, currently smoking, or who have a family history of osteoporosis.

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