What is a DXA scan? 

A dual energy X-ray absorptiometry scan (DXA, previously DEXA) is a specialised X-ray technique, which specifically measures bone mineral density (bone mineral content) and provides the most accurate way to assess this. This is just like a normal X-ray, with no pain involved.

It is used to:

• confirm the diagnosis of osteoporosis
• estimate severity of bone loss
• determine whether the patient is responding to treatment

It is a fast scan, has high resolution, is easily reproducible and has a lower radiation dose compared to other methods. Usually only the lumbar spine (lower back) and proximal femur (hip region) are measured.

Interpretation of DXA scan results

The result of a DXA scan is presented as a T-score. This reflects how much your bone density differs from that of a healthy young woman (when peak bone mass is at its best), measured in 'standard deviations'. A more negative T-score represents a more reduced bone density. In general, for every one standard deviation reduction in T-score, the risk of fracture doubles: i.e. someone with a T-score of -2 faces twice the risk of fracture of someone whose T-score is -1.

The important aspect of this measure is that it quantifies loss of bone mineral density in the skeleton at the site of measurement. It is this loss of bone mineral density that leads to osteoporosis.

There are stages in the progression of bone mineral density loss that eventually lead to osteoporosis. The majority of DXA studies measure bone mineral density at two sites – the hip and spine.

DXA Results

Normal Osteopaenia Osteoporosis A normal bone density is when the T score measures greater than –1.0 (greater than minus 1.0) If the bone mineral density is measured as a T score between  –1.0 and –2.5 (minus 1.0 and minus 2.5) this indicates the presence of osteopaenia. Osteopaenia is not osteoporosis. It does however indicate that there is a reduction in bone mineral density, which is not as severe as osteoporosis. This condition represents an earlier phase of bone mineral density loss in the skeleton. If the bone mineral density is measured as a T score of –2.5 or less (minus 2.5 or less) this indicates the presence of osteoporosis at the site of measurement.

It is important to realise that a low bone mineral density measure is associated with an increased risk of fractures. However, even when a woman does have a finding of a low bone density on a DXA scan, it does not mean she is going to have a fracture. Other factors influence the likelihood of fracture, not just the bone mineral density reading on a DXA scan. For instance, a woman in her 50s or 60s whose DXA scan indicates osteoporosis, but who is healthy, is less likely to have a fracture than a woman in her 80s whose DXA scan indicates osteoporosis and show has a tendency to fall due to other medical conditions.

Who should have a DXA scan?

People who have an increased risk of osteoporosis should talk to their doctor about having a DXA scan. A doctor’s referral is required for a DXA. Not all people will be eligible for the full Medicare rebate.

The cost of a DXA scan is approximately $85.00. The cost may vary depending on where the test is performed. There are specific indications that allow for a Medicare rebate in Australia. These include:

• People aged 70 years and over
• 1 or more fractures occurring after minimal trauma
• Monitoring of low bone mineral density proven by previous bone DXA
• Prolonged steroid therapy
• Female hypogonadism (oestrogen deficiency) lasting more than 6 months before age of 40.
• Male hypogonadism (testosterone deficiency)
• Primary hyperparathyroidism
• Chronic liver disease
• Chronic kidney disease
• Proven malabsorption disorders, e.g. Coeliac disease
• Rheumatoid arthritis
• Hyperthyroidism

Frequency of DXA scan

Generally your doctor will arrange for you to have a repeat DXA scan every two years to monitor the status of your bones or assess the effects of therapy. It is also important to have the DXA scan performed on the same machine, to allow for accurate comparison of results.

Content updated July 22, 2011