What does a DEXA scan tell you that a regular bone density measurement does not?
A DEXA scan provides an accurate number for bone density at the clinically most relevant sites, plus body composition and a standardised diagnosis -- none of which a standard X-ray can offer.
A regular X-ray shows what bones look like, but provides no number for how dense and solid they are. Bone loss only becomes visible on such an image once roughly 30% of bone mass has already disappeared. DEXA measures bone mineral density quantitatively at the sites that matter most: the spine, the hip, and optionally the whole body. This allows it to detect bone loss at an early stage, long before a standard X-ray reveals anything.
The WHO uses a T-score of -2.5 or lower on a DEXA scan as the official threshold for a diagnosis of osteoporosis. That T-score compares your bone density with that of healthy young adults. A standard X-ray yields no T-score, making standardised diagnosis and treatment decisions impossible. Of 52 national guidelines across 36 countries, more than half incorporated a fracture-risk calculation based in part on DEXA data.
Older methods could only measure bone density at the wrist or heel, the peripheral extremities of the skeleton. DEXA can image the spine from the front and the side, the hip, and the whole body; it offers better precision, stable calibration, a low radiation dose, and larger reference databases. On top of that, DEXA also measures body composition: how much fat and how much muscle mass you have, and whether vertebral fractures are present.
DEXA also has clear limitations. It produces no three-dimensional image and says nothing about the fine internal structure of bone tissue, the so-called microarchitecture. As a result, fracture risk can be underestimated, particularly in people whose bone structure is already compromised but whose density still looks reasonably normal. Newer techniques such as quantitative CT can provide that information, but are not yet standard practice in the clinic.
In children and adolescents, additional caveats apply: the growing skeleton makes interpretation more complex, and a diagnosis of osteoporosis in this group is never based solely on a DEXA measurement.
Based on several diagnostic reviews and guideline analyses (PMID 21440697, 28734709, 11537603, 10986616, 30177358, 30086870). No RCTs; this concerns diagnostic evaluation and method comparison.
Does being overweight affect your bone density?
Being overweight does not straightforwardly increase bone density, and the location and amount of fat strongly determine whether the skeleton benefits or is harmed. If you are considering losing weight, do so gradually and combine it with strength training to limit bone loss.
How much impact does smoking have on your bone density?
Smoking substantially increases the risk of bone loss and hip fractures; quitting helps, but it takes at least ten years before your fracture risk decreases noticeably.
Can adults still build bone mass, or only maintain it?
As an adult you can still build bone mass, although the gains are more modest than in earlier life. Strength training, at least three times per week at high intensity, has the best evidence base for this.
Is there a link between sleep deprivation and bone loss?
Sleep deprivation and poor sleep quality are associated with reduced bone formation and, in postmenopausal women, considerably greater bone loss. Getting enough regular sleep is therefore also relevant to your bone health.
What do bone-loss medications (bisphosphonates) do, and are they safe?
Bisphosphonates reduce fractures and increase bone density in osteoporosis, and at high fracture risk can be used safely for up to ten years, provided that dental procedures are discussed with your doctor in advance.
Can eating disorders such as anorexia cause permanent bone damage?
Anorexia causes permanent bone damage in the majority of cases, particularly when the condition begins during adolescence. Discuss a bone assessment with your doctor if you or someone you know is affected by this.