INTERPRETING DXA SCORES
DXA (dual energy x-ray absorptiometry) scans are used to measure bone mineral density, which is a measure of bone health. Low bone mineral density is associated with a higher risk of bone stress injury in distance runners, and bone density loss is correlated with an increased risk of all-cause fracture.
Most of the time young people don’t have to think about this - this is an older person’s problem, right? Not necessarily. Younger individuals, particularly athletes who have experienced recurrent bone stress injuries and/or have a history of eating disorder, are often familiar with bone injuries and the subsequent DXA scans to assess bone health.
DXA results are reported as T-scores for post-menopausal women and men over age 50, and as Z-scores for children, premenopausal women, and men under age 50.
Interpretation of these scores, particularly in individuals between ages 20-50, can be a bit confusing as the resulting classification varies depending on an individual’s age, injury history, health history and current health & athletic status.
Below is a chart with the International Society for Clinical Densitometry’s (ISCD) official interpretations of DXA Z-scores findings in individuals from 20-50 years old.
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Unfortunately, an individual’s fracture history, eating disorder status or history, and other secondary causes of bone density loss are not included in a DXA report - so based on these guidelines, it is possible for a test that actually shows significant bone density loss to be interpreted as “within normal limits”.
In addition, caution must be utilized when interpreting these scores in athletes. Athletes should have 5-15% higher bone density than non-athletes because of the load they’re exposing their bones to during practice & competitions. Both the International Olympic Committee and the American College of Sports Medicine define normal bone mineral density in athletes as -1.0 or greater, one full standard deviation higher than the ISCD’s cutoff score for what’s considered normal.
Because of the significant negative health consequences that could result from a provider missing low bone density in an athlete, DXA results need to be interpreted within the context of the individual’s current health status & health history.
According to Dr. Jennifer Gaudiani, medical doctor and author of the book Sick Enough: A Guide to the Medical Complications of Eating Disorders, DXA is indicated in the following situations:
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Within 1 year when a female patient loses her period
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Within 1 year of the start of restrictive behaviors in individuals with anorexia nervosa
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Following a long bone fracture
If you’ve been diagnosed with low bone density for your age, it is possible to improve it even beyond your late 20s - fueling, strength training, plyometrics and weight (and more!) all play a role in bone health, and since bone is an adaptable, living tissue, it continues to respond and change over time! Improving bone density can reduce your risk for future stress fracture, making training and racing more consistent and enjoyable.
Looking for a physical therapist to help you rehab from a bone stress injury, or a running coach to help you avoid future bone stress injuries? Let’s chat! Click the button below to reach out.
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References:
Gaudiani, J. L. (2018). Sick enough: A guide to the medical complications of eating disorders. Routledge.
Lewiecki et al. 2008. International Society for Clinical Densitometry 2007 adult and pediatric official positions. Bone, 43(6), 1115-1121.
Duckham et al. 2014. Does physical activity in adolescence have site specific and sex specific benefits on young adult bone size, content, and estimated strength?. Journal of bone and mineral research, 29(2), 479-486.