DEXA Scan Results

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DEXA Scan Results

Question:

When given the results of a DEXA scan for osteoporosis, what do the numbers represent?

Answer:

The DEXA scan is a type of X-ray that estimates bone mineral density, which is a measure of bone strength. It's the most common screening test for osteoporosis, a condition in which bone density is low and the risk of bone fracture is increased.

In most cases, the important numbers to know are your T-scores. These are measures of your bone density compared to young adults considered to have "normal" bone density. The lower your T-score, the higher your fracture risk. Here's how T-scores are reported:

• -1.0 and higher are normal.

• -1.0 to -2.5 indicate osteopenia (reduced bone density, but not as low as osteoporosis).

• -2.5 and below indicate osteoporosis (significantly low bone density).

Results can also be described as Z-scores. These are measures of bone density that compare your bone density with that of people your age and gender. If you're a 56-year-old woman, you could have low bone mineral density, but because so many women your age have low bone mineral density, your Z-score might be normal. That's why it's usually best to assess how low bone mineral density is compared with "normal" rather than compared with others your age. And that's why T-scores are generally most helpful.

Finally, your results may include the actual bone mineral density, expressed as a number that is less than one (such as 0.771). This is the readout from the DEXA machine. It is related to bone absorption of the X-ray energy. Although this number is used to create the T- and Z-scores, it isn't as helpful as T- and Z-scores scores in interpreting the results.

The risk of fracture increases with lower bone mineral density. The actual risk of fracture can be calculated based on bone mineral density results. For example, if you had a T-score of -2.1 and a Z-score of -1.6, the 10-year risk of hip fracture is about 1%. However, there are many other factors that go into measuring fracture risk besides bone mineral density results, including:

• History of prior fracture

• Family history of osteoporosis

• Calcium and vitamin D intake

• Alcohol intake and smoking history

• Medication use (especially corticosteroids)

Besides modifying these risk factors whenever possible (e.g., stop smoking), doctors routinely recommend weight-bearing exercise and calcium and vitamin D supplements for post-menopausal women. Other medications, such as alendronate (Fosamax) or risedronate (Actonel) may be recommended if bone density is low or falling over time. Talk to your doctor about your results and decide together on a treatment plan.

Robert Shmerling, M.D., is associate physician and clinical chief of rheumatology at Beth Israel Deaconess Medical Center and an associate professor in medicine at Harvard Medical School. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program and has been a practicing rheumatologist for over 25 years.

Last updated:	July 20, 2009