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by Irwin Lim, Rheumatologist

It’s not perfect, but DXA (also known as DEXA) is still the gold standard for diagnosing osteoporosis. A combination of convenience, safety and low cost means it’s still the best we have.

What is it?

DXA or dual energy X-ray absorptiometry uses two X-ray beams to work out how strong bones are. As the X-rays pass through the body, the X-rays are weakened to a different extent in the different tissues of the body. This allows the calculation of bone mineral density (BMD).

BMD is measured typically as the spine and the hip, and on some occasions, at the forearm. This bone density is compared to that of healthy young adults (T-score), and to that of an average person of the same age, gender and ethnicity (Z-score). These scores help us determine if a person has Osteopenia, low bone density, or Osteoporosis.

DXA is safe and quick, taking about 15 minutes. It is painless and involves lying on a bed. There is a small amount of radiation exposure involved, but this is less than that of a chest X-ray.

When should DXA be performed?

It makes sense to investigate people who are at risk of bone loss. These include conditions such as premature menopause, rheumatoid arthritis, prolonged use of steroids, chronic liver and kidney disease, malabsorption disorders and a variety of hormonal diseases. The risk of low bone density is higher in the elderly, and it’s recommended that people over 70 be tested.

In addition to the above, anyone who has suffered a fracture without a history of significant trauma (minimal trauma fracture) should have the test.

Why bother?

DXA is still the simplest way to detect weakening of the bones, with the most severe form of this called osteoporosis. A DXA is important for diagnosis. It can be used to help monitor treatment. The data generated helps calculate the future risk for fracture.

The goal is of course to improve or at least, slow the decline in bone density and strength. The ultimate aim is to prevent fractures, avoiding unnecessary pain, suffering and loss of independence.

Do you have risk factors for low bone density? If so, ask your doctor if you should have DXA testing.

Dr Irwin Lim is a rheumatologist and a director of BJC Health. You should follow him on twitter here.
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