What does a DEXA scan reveal that a standard bone density measurement does not?
A DEXA scan offers far more than a single density figure: it also images vertebral fractures, bone structure, muscle mass, and even signs of cardiovascular risk. If you want to know how strong your bones truly are, a DEXA scan is the most comprehensive routine option available.
A standard X-ray can show bones, but gives no figure for how dense and strong they are. A DEXA scan does exactly that: it measures bone mineral density at the sites that matter most for fracture risk, namely the spine and hip. The result is expressed not only as a number in grams per square centimetre, but also as a so-called T-score: a comparison with the average bone density of young, healthy adults. On the basis of that score, the World Health Organization makes the diagnosis of osteoporosis.
Modern DEXA machines also image the spine in a way that makes small, sometimes painless vertebral fractures visible. Such a fracture is in itself a sign of an increased risk of new fractures, even when the T-score is not yet alarming. That is therefore information that a bone density figure alone does not provide.
In addition, the DEXA scan calculates something that can be thought of as a texture analysis of the spongy bone tissue deep inside. That texture, separate from bone density, says something about how well the bone is organised and whether it can withstand load. Two people with the same bone density can still have very different fracture risks, and the texture score helps to refine that distinction.
Furthermore, a DEXA scan measures total body composition: how much fat you have, and how much muscle mass. This is relevant if you want to know whether age-related muscle loss is present, a condition that is sometimes accompanied by an increased risk of falls. As a secondary finding, the scan can also detect calcium deposits in the large abdominal aorta, a risk factor for cardiovascular disease, although that is not the primary purpose of the scan.
The DEXA scan does, however, have its limits. It produces a flat, two-dimensional image and cannot say anything about the fine structure of bone at the microscopic level. Bone size also plays a role: larger bones automatically appear denser on a DEXA scan. This can sometimes lead to a skewed result, in people whose bone size differs from the average or in people with a great deal of calcification visible on the image.
This answer is based on multiple review articles about DXA as a diagnostic tool. The added value of DEXA over a standard X-ray is well described and widely accepted. The additional applications, such as the texture score and vertebral fracture analysis, rest on a less extensive body of literature but have been clinically introduced and recognised. The reviewers are equally consistent regarding the limitations of DEXA compared with newer three-dimensional techniques.
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 lasting bone damage?
Anorexia can cause lasting bone damage, especially when the illness begins during puberty. Early recovery is crucial; speak with your doctor about this if you or someone you know is affected.