DEXA (dual-energy X-ray absorptiometry) is a type of X-ray that measures bone mineral density (BMD). It uses two low-energy X-ray beams to assess how dense your bones are. The scan is quick, painless, and uses very little radiation. Results are expressed as T-scores — a comparison against peak bone density in healthy young adults — to determine whether bone density is normal, reduced (osteopenia), or in the osteoporosis range.

Does a DEXA scan hurt?

No. A DEXA scan is completely painless. You lie on a flat table, fully clothed, while a scanning arm passes slowly over you. The scan takes around 10–20 minutes. No needle, contrast agent, or preparation is required. Radiation exposure is very low — roughly equivalent to a few hours of natural background radiation.

What does my T-score mean?

Your T-score compares your bone density to a young adult of the same sex at their peak bone mass. A T-score above −1.0 is normal. Between −1.0 and −2.5 indicates osteopenia — below-average bone density but not yet in the osteoporosis range. A T-score of −2.5 or below indicates osteoporosis. Your clinician will interpret the T-score alongside your other risk factors — a T-score alone does not determine whether treatment is needed.

Who should have a DEXA scan?

Recommended groups include women aged 65 and over, postmenopausal women under 65 with risk factors such as family history, low body weight, or prior fracture, men aged 70 and over, and anyone who has had a fragility fracture (a fracture from a minor fall or without significant trauma). People taking long-term corticosteroids and those with conditions that affect bone health should also be assessed. If you are unsure, ask your GP.

How often should I have a DEXA scan?

Frequency depends on your results and risk profile. If your first scan is normal and risk is low, a repeat in 5–10 years may be sufficient. If you are being treated for osteoporosis, monitoring every 1–2 years is typical to assess treatment response. Follow your clinician's advice on timing.

Can osteoporosis be treated?

Yes. Treatment can increase bone density and substantially reduce fracture risk. Options include weight-bearing exercise, adequate calcium and vitamin D, fall prevention strategies, bisphosphonate medications, denosumab, hormone therapy, and — for severe cases — anabolic agents. Earlier detection and treatment lead to better outcomes.

Bone Density Testing (DEXA): Who Should Be Screened and When

What Is DEXA?

DEXA — dual-energy X-ray absorptiometry — is the internationally accepted standard for measuring bone mineral density (BMD). It uses two low-energy X-ray beams at different energy levels that pass through bone and soft tissue. Because bone and soft tissue absorb these energies at different rates, the scanner can calculate precisely how much mineral (primarily calcium phosphate) is contained within the bone — separately from the surrounding muscle and fat.

DEXA is painless, quick, and uses very little radiation — approximately 1–6 microsieverts per scan. For comparison, a chest X-ray delivers around 100 microsieverts and an abdominal CT scan around 10,000–50,000 microsieverts. Flying from Sydney to London delivers approximately 80–100 microsieverts.

The scan is typically performed on two sites:

Lumbar spine (lower back, L1–L4) — the most sensitive site for detecting early bone loss and monitoring treatment response
Proximal hip (femoral neck and total hip) — the most clinically important site for fracture risk and the most reproducible between different scanners

Key Points

DEXA is the standard test for measuring bone mineral density and diagnosing osteoporosis.
The scan is painless, takes 10–20 minutes, and uses very low radiation — far less than a chest X-ray.
Results are expressed as T-scores compared to a young-adult reference population.
WHO diagnostic categories: normal (T-score above −1.0), osteopenia (−1.0 to −2.5), osteoporosis (−2.5 or below).
All women aged 65 and over and all men aged 70 and over should be offered DEXA; earlier screening applies when significant risk factors are present.
Women experience the most rapid bone loss in the first 5–10 years after menopause — this is the period of highest risk.
A T-score alone does not determine treatment; the FRAX fracture risk calculator combines T-score with clinical risk factors.
Osteoporotic fractures — particularly hip fractures — carry a one-year mortality of around 20–30%.
Treatment is effective: bisphosphonates reduce vertebral fracture risk by 40–70% and hip fracture risk by approximately 40%.

How DEXA Works

When the two X-ray beams pass through your body, a detector measures how much of each beam is absorbed. Bone attenuates (absorbs) the beams differently from soft tissue, and the higher-energy beam differentiates bone from fat more precisely. Software processes these differences to calculate bone mineral content (BMC, in grams) and areal bone mineral density (BMD, in grams per square centimetre) at each site measured.

The scanner then compares your BMD against a stored reference population to produce two scores:

T-score — compares your BMD to the average BMD of a healthy young adult of the same sex at their peak bone mass (typically around ages 25–30). This is the score used to diagnose osteoporosis according to WHO criteria.

Z-score — compares your BMD to age-matched peers (people of the same age, sex, and sometimes ethnicity). A Z-score below −2.0 suggests bone loss greater than expected for your age and prompts investigation for secondary causes of bone loss, such as long-term steroid use, coeliac disease, hyperparathyroidism, or other conditions.

What to Expect During the Scan

Wear comfortable, loose clothing without metal fixtures in the scan area; a hospital gown is sometimes provided
Remove belt buckles, zips, and underwire in the area to be scanned
Lie flat on a padded table; the scanning arm passes slowly over your lower back and hip
Each site takes approximately 3–7 minutes; total scan time is usually 10–20 minutes
No needles, contrast agents, claustrophobia, or special preparation required
If you have recently had a barium study, nuclear medicine scan, or intravenous contrast, inform the radiographer — some agents can temporarily affect DEXA accuracy
Inform the radiographer if there is any possibility of pregnancy

Results are reported by a radiologist, and a written report is sent to your referring clinician.

Understanding Your Results

WHO Diagnostic Categories (Based on T-score)

T-score	Diagnosis	Implications
Above −1.0	Normal	Bone density within the expected range for a young adult
−1.0 to −2.5	Osteopenia	Below-average bone density; elevated fracture risk compared with normal, but not in the osteoporosis range
−2.5 or below	Osteoporosis	Significantly reduced bone density; high fracture risk; treatment discussion warranted
−2.5 or below + fragility fracture	Severe osteoporosis	Highest risk category; fracture has already occurred

Important: A T-score in the osteopenia range does not automatically mean treatment is required. Many people with osteopenia have a low absolute fracture risk and are managed well with lifestyle measures and monitoring. Treatment decisions are based on overall fracture probability, not T-score alone.

The FRAX Fracture Risk Tool

FRAX (Fracture Risk Assessment Tool) is a WHO-developed calculator that estimates a person’s 10-year probability of a major osteoporotic fracture (spine, forearm, hip, or shoulder) and hip fracture specifically.

FRAX incorporates:

Age, sex, and body weight
Femoral neck T-score (from DEXA)
Prior fragility fracture
Parental history of hip fracture
Current smoking and alcohol use
Glucocorticoid use
Rheumatoid arthritis
Secondary causes of osteoporosis

A FRAX probability above a locally defined intervention threshold is used to guide treatment decisions, particularly for people with osteopenia whose T-score alone does not meet the treatment threshold. Your clinician can calculate FRAX alongside your DEXA result.

Who Should Be Screened

Group	Recommendation
Women aged 65+	DEXA recommended for all
Men aged 70+	DEXA recommended for all
Postmenopausal women under 65 with risk factors	Discuss with GP; risk factors include prior fracture, family history, low body weight, early menopause
Men aged 50–69 with multiple risk factors	Discuss with GP
Anyone with a fragility fracture (low-trauma fracture)	DEXA recommended regardless of age
Long-term corticosteroid use (≥3 months at ≥7.5 mg/day prednisone equivalent)	DEXA recommended; steroids are the most common drug cause of osteoporosis
Early menopause (before age 45) — natural, surgical, or chemotherapy-induced	Earlier DEXA warranted; earlier oestrogen loss means earlier bone loss
Aromatase inhibitor therapy (used in breast cancer)	Assess bone density; these agents accelerate bone loss
Androgen deprivation therapy (used in prostate cancer)	DEXA recommended; significant bone loss occurs with testosterone suppression
Conditions associated with bone loss — coeliac disease, inflammatory bowel disease, hyperparathyroidism, chronic kidney disease, eating disorders	Discuss with GP

In Australia, Medicare provides a rebate for DEXA scanning in eligible patients. Your GP can determine eligibility and provide a referral.

Risk Factors for Low Bone Density

Understanding risk factors helps identify who needs earlier or more frequent screening.

Non-modifiable:

Female sex — women have lower peak bone mass and experience rapid bone loss after menopause
Increasing age
White or Asian ethnicity
Family history of osteoporosis or hip fracture
Prior fragility fracture — itself the single strongest predictor of future fracture
Early menopause (before age 45), whether natural, surgical, or chemotherapy-induced

Modifiable:

Physical inactivity — particularly lack of weight-bearing and resistance exercise
Low dietary calcium intake
Vitamin D deficiency — common in older adults with limited sun exposure
Smoking
Excess alcohol (more than 2 standard drinks per day on average)
Low body weight (BMI below 20)
Prolonged bed rest or immobility

Medical conditions and medications:

Long-term corticosteroid use — the most common drug cause of secondary osteoporosis
Aromatase inhibitors (breast cancer treatment)
Androgen deprivation therapy (prostate cancer treatment)
Anticonvulsants (some accelerate vitamin D metabolism)
Coeliac disease, Crohn’s disease, other malabsorption syndromes
Hyperparathyroidism, hyperthyroidism
Chronic kidney disease
Hypogonadism (low sex hormones in men or women)
Rheumatoid arthritis
Eating disorders, particularly anorexia nervosa

Menopause and Bone Loss

Bone loss accelerates dramatically in the years following menopause — this is the period of greatest risk for most women, and the strongest clinical rationale for DEXA screening in women before age 65 when risk factors are present.

Why menopause affects bones:

Oestrogen is essential for maintaining the balance between bone formation (osteoblasts) and bone resorption (osteoclasts). As oestrogen levels fall at menopause, osteoclast activity increases without a compensating rise in osteoblast activity. The result is net bone loss.

Women lose approximately 1–3% of bone mass per year in the first 5–10 years after menopause
Cumulative bone loss over this period can reach 15–20%
By age 70, a woman may have lost 30–40% of her peak bone mass

Implications for screening:

Women with early menopause (before age 45) begin bone loss earlier, have a longer exposure window, and should be screened earlier
Women approaching or recently past menopause with additional risk factors should not wait until age 65 for their first DEXA
Hormone therapy (HRT/MHT) can prevent menopausal bone loss and reduce fracture risk; this is an individualised decision made with a clinician, balancing bone protection against other considerations

After Your Results — What Happens Next

Normal result (T-score above −1.0): Reassurance and lifestyle reinforcement — adequate calcium, vitamin D, weight-bearing exercise. A follow-up DEXA in 5–10 years is usually appropriate depending on age and risk profile.

Osteopenia (T-score −1.0 to −2.5): FRAX calculation to determine absolute 10-year fracture risk. If risk is low, lifestyle measures, calcium and vitamin D optimisation, and a follow-up DEXA in 2–5 years. If FRAX risk exceeds the intervention threshold, pharmacological treatment is discussed.

Osteoporosis (T-score −2.5 or below): Treatment discussion. First-line pharmacological options include bisphosphonates (alendronate, risedronate, zoledronic acid). Additional measures include calcium and vitamin D supplementation, resistance and balance exercise, fall prevention review, and specialist referral in complex cases. Monitoring DEXA every 1–2 years during treatment assesses response.

Fragility fracture — regardless of T-score: A fracture from a minor fall or without trauma is itself a medical priority. A fracture liaison service (FLS) — where available — coordinates post-fracture bone health assessment and treatment to prevent subsequent fractures. The risk of a second fracture is highest in the 1–2 years immediately following the first.

Limitations of DEXA

DEXA is the best available clinical tool for bone density measurement, but it does not capture everything:

Bone quality and microarchitecture — T-score reflects density but not the internal trabecular structure of bone. Two people with identical T-scores can have different fracture resistance depending on bone geometry and microstructure.
Vertebral fractures are not always detected — standard DEXA does not diagnose vertebral compression fractures, which are often silent. Vertebral fracture assessment (VFA) can be added to most modern DEXA scans and is worth requesting if vertebral fracture is suspected.
Peripheral DEXA (wrist, heel) — portable devices scanning peripheral sites are less accurate and not used for definitive diagnosis or treatment decisions; full spine and hip DEXA is required.
Machine variability — T-score results can vary between different DEXA machines. For serial monitoring, ideally use the same machine at the same facility to ensure comparability.
Artefacts — severe scoliosis, calcified aorta, or degenerative disc disease can falsely elevate lumbar spine T-scores. Hip measurements are usually more reliable when spinal artefact is present.
Severe obesity — very high body weight may reduce scan accuracy; the hip is typically more reliable than the spine in this situation.