Bone loss can develop without obvious symptoms. For some people, a fracture may be the first indication that bone strength has reduced. Bone density testing gives clinicians a measurement of bone mineral density (BMD) that can be considered alongside other factors when assessing fracture risk.

DEXA, or dual-energy X-ray absorptiometry, is the standard method used to measure bone mineral density at sites such as the hip and lower spine. This article explains what the test measures, who may be considered for testing in Australia, what the results mean, and what to expect during the scan.

What Is a Bone Density Test?

Bone Density and Bone Mineral Density

Bone density testing measures bone mineral density, usually abbreviated to BMD. The measurement provides information about the amount of mineral contained within a defined area of bone and can help identify reduced bone density.

Lower bone mineral density is associated with an increased risk of fracture and may be seen in people with osteoporosis. A bone density result is not the same thing as a complete assessment of fracture risk, because other factors such as age, previous fractures, medicines and falls risk also matter.

How Does a DEXA Scan Work?

DEXA uses two low-dose X-ray beams to estimate bone mineral density. During a central DEXA scan, you normally lie on a padded table while the scanning arm passes over the body. The hip and lumbar spine are commonly measured.

The procedure does not usually involve needles, injections or contrast dye. It uses a small amount of ionising radiation. Your imaging provider can explain the radiation dose and any preparation requirements for the equipment being used.

Why Is Bone Density Testing Useful?

Bone density testing can provide objective information that may help a clinician decide whether further assessment, monitoring or treatment should be considered.

A lower BMD result does not mean that a fracture is inevitable, and a normal result does not eliminate every risk factor for fracture. The result needs to be interpreted in the context of your overall health and clinical history.

Who May Need a Bone Density Test?

Australian guidance identifies several groups in whom bone density assessment may be appropriate. The decision should be based on clinical circumstances rather than age alone.

Groups commonly considered for assessment include:

• People aged 70 and over.
• People who have sustained a minimal-trauma fracture, such as a fracture following a fall from standing height or a similarly low level of force.
• People over 50 with relevant risk factors, which may include a family history of hip fracture, early menopause, rheumatoid arthritis and some chronic medical conditions.
• People with suspected vertebral fracture or other circumstances that may indicate increased fracture risk.

Other factors can influence whether testing is appropriate, including some endocrine or gastrointestinal conditions, diabetes, chronic kidney or liver disease and prolonged corticosteroid use. Menopause and other hormonal changes can also affect bone loss.

The exact indications for testing can change according to the individual’s history, current treatment and relevant Australian guidance. Your GP can assess your fracture risk and determine whether bone density testing is appropriate.

Medicare and Cost

Medicare rebates for bone densitometry are available in defined circumstances. Eligibility depends on the relevant Medicare Benefits Schedule (MBS) requirements, including the clinical indication and, for some items, the timing of previous scans.

Because eligibility and out-of-pocket costs can depend on the specific circumstances, it is sensible to ask your GP which MBS item may apply and to confirm any fees with the imaging provider before booking.

View the MBS information on bone densitometry items.

Types of Bone Density Testing

DEXA: The Standard Method

Central DEXA is the standard method used to assess bone mineral density for clinical purposes. It commonly measures the lumbar spine and hip and provides results that can be interpreted using established diagnostic criteria.

Peripheral bone density devices can measure sites such as the heel, wrist or finger. These tests can have a role in some screening settings, but they are not equivalent to a central DEXA scan for diagnosis.

Quantitative CT

Quantitative computed tomography can assess bone density in three dimensions and may be useful in selected circumstances. CT involves more radiation than DEXA and is not routinely used as the first-line method for bone mineral density measurement.

What About MRI?

MRI does not use ionising radiation and can be valuable for imaging soft tissues and detecting some fractures. However, it is not the routine test used to measure bone mineral density.

What Happens on the Day?

Preparation

Preparation requirements vary between imaging providers. You may be asked to wear comfortable clothing and remove metal objects such as belts or jewellery because these can interfere with imaging.

Some providers may ask you to temporarily avoid calcium supplements before the scan. Follow the instructions given by the imaging practice when you book.

Tell the imaging provider if you are pregnant or might be pregnant. Also mention recent imaging involving contrast material or nuclear medicine, as this may affect the timing of the test.

The Scan

A trained medical imaging professional will position you on the scanning table and explain the procedure. You generally remain still while the scanner passes over the relevant areas.

A central DEXA scan is usually brief and painless, although the exact appointment length varies between providers and the type of assessment being performed.

The report is generally sent to the referring clinician, who can interpret the result alongside your history and other fracture-risk factors.

Understanding Your Results

T-Scores

A T-score compares your bone mineral density with the average peak bone mineral density of a healthy young adult. For postmenopausal women and men aged 50 and over, commonly used diagnostic thresholds are:

• Above -1.0: within the normal range.
• From -1.0 to -2.5: low bone density, commonly described as osteopenia.
• -2.5 or lower: meets the densitometric criterion for osteoporosis.

These thresholds are used within a broader clinical assessment and do not, on their own, predict whether an individual will experience a fracture.

Z-Scores

A Z-score compares bone mineral density with people of a similar age and sex. A Z-score of -2.0 or lower may be described as below the expected range for age and can prompt investigation for possible secondary causes, depending on the clinical context.

What the Numbers Do and Do Not Tell You

A lower BMD is associated with higher fracture risk, but bone density is only one component of that risk. Previous fractures, age, family history, medicines, other medical conditions and the risk of falling may all contribute.

A result in the osteopenia range is not the same as a diagnosis of osteoporosis, and a diagnosis of osteoporosis does not mean that a fracture is certain.

For people already being monitored or treated for low bone density, repeat scans may be used to assess change over time. Because bone-density changes are usually gradual and small differences can reflect measurement variation, repeat testing is generally performed at clinically appropriate intervals rather than very frequently.

Looking After Your Bones

Many of the factors that support bone health are relevant whether or not you have had a DEXA scan.

Adequate calcium and vitamin D are important for normal bone health. Weight-bearing activity and resistance exercise can provide mechanical loading for the skeleton, while balance training can help reduce falls risk.

Smoking and higher alcohol consumption are associated with poorer bone health. Australian alcohol guidelines recommend that healthy adults drink no more than 10 standard drinks per week and no more than 4 standard drinks on any one day.

If medication is being considered for osteoporosis or fracture prevention, that decision should be based on an overall assessment of fracture risk and the individual’s circumstances rather than on the scan result alone.

Where to Have a Bone Density Scan

Bone density scanning is available through radiology practices across Australia. When arranging a scan, you can ask whether the service performs central DEXA, what preparation is required, and what out-of-pocket costs may apply.

For follow-up scans, using the same facility and, where practical, the same equipment can make comparison over time easier because measurements can vary between machines and techniques.

If you are unsure whether bone density testing is appropriate for you, a consultation with a qualified health practitioner can help assess your history and fracture-risk factors and determine whether a referral is indicated.

In Summary

A DEXA scan provides a useful measurement of bone mineral density and can form part of a broader assessment of fracture risk. It is most relevant for people with age-related or clinical risk factors for low bone density, including older adults and people who have experienced a minimal-trauma fracture.

A scan should not be viewed as a stand-alone verdict on bone health. The result is interpreted alongside your medical history, medicines, previous fractures, falls risk and other relevant factors.

If you think you may be at increased risk of osteoporosis or fracture, speak with your GP about whether bone density testing is appropriate and whether you may be eligible for a Medicare rebate.

This article is general information only and is not medical advice or a diagnosis. Bone density testing should be considered in consultation with a qualified health practitioner, who can advise whether it is appropriate for you and interpret the results in the context of your health. Individual circumstances and results vary.