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Common sense DXA reporting

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The current method of reporting DXA results leads to undue worry for patients and clinicians.

The bone mineral density data is presented to three decimal places as gm/cm². What’s wrong with reporting a whole number as mg/cm²?

Reference intervals for reporting most clinical lab data encompass the 95% confidence intervals — from two standard deviations below the mean (Z-score –2.0) to two standard deviations above the mean (Z-score +2.0). For DXA, we use three cut-points (< –1.0, –1.0, –2.5, and < –2.5). Worse yet, we use T-score and Z-score which adds to some of the confusion for our patients.

A committee of the World Health Organization developed these cut points in the early 1990s when DXA was still in its infancy. Since then, abundant epidemiologic data has repeatedly noted that most osteoporosis-related fractures occur in patients in whom the BMD is not < –2.5, and it's time to fix the system.

Why my concern now? Because I have just read yet another peer-reviewed article reporting that a substantial percentage of women with vertebral fractures had “osteopenia” but not as many as those who had “osteoporosis.” At face value, the article could be confirming that osteoporosis-related fractures can occur in women with a T-score better than –2.5. Regrettably that was not the message the authors wanted to convey because the discussion and conclusions simply did not acknowledge that once the patient has a fragility fracture the diagnosis is osteoporosis independent of the T-score classification.

The terminology matters to me because I see patients with “osteopenia,” no matter where on the T-score spectrum, who had been placed on therapy without a very clear understanding that it is needed, and referred when the BMD has not changed over a two-year period. I, and I suspect many of you, also see patients with fractures in whom the diagnosis of osteoporosis is not made because the T-score doesn’t match.

Will the latest WHO offering — the Fracture Risk Assessment Tool or FRAX — solve the problem? Probably yes but not in the short term. Visit the website (http://www.shef.ac.uk/FRAX/index.htm) and spend some time on the FAQ page. This will provide you with answers to many of your current questions (not always what you want to hear) and an understanding that this is still a work in progress.

FRAX will go a long way to ensuring that patients with prior fractures are recognized as being at greater risk of subsequent fracture than those without a fracture history. If you take an appropriate history from the patient, you won’t need a numerical tool to make your treatment decision.