What Is a DXA Scan?

A DXA scan is the standard medical test used to measure bone density. You may see it written as a DEXA scan, a bone density scan or bone densitometry — these are all the same test. It is the only way to reliably diagnose osteoporosis, and it is used to assess fracture risk and to monitor how well treatment is working over time.

If you already have an appointment and want to know about cost, medical card cover or waiting times, see how to get a DXA scan in Ireland.

What Does DXA Stand For?

DXA stands for Dual-energy X-ray Absorptiometry. You may also see it written as DEXA. The scan uses two low-energy X-ray beams of different energies to measure how much energy the bone absorbs. The denser the bone, the more energy is absorbed. This gives a precise measurement of bone mineral density (BMD).

What Does a DXA Scan Measure?

A DXA scan measures bone mineral density (BMD) — the amount of mineral (primarily calcium and phosphate) in a given area of bone. It is typically performed at two sites:

• The hip (femoral neck and total hip) — the most clinically significant site for fracture risk
• The lumbar spine (lower back, typically L1–L4) — useful for detecting early bone loss

In some cases, the wrist (distal radius) may also be scanned, particularly if the hip or spine results cannot be used (e.g., due to previous surgery or severe arthritis).

What Does a DXA Scan Show?

A DXA scan produces one number and two comparisons. The number is your bone mineral density in grams per square centimetre. The comparisons are what your doctor actually reads:

• Your T-score — how your bone density compares with a healthy young adult at peak bone mass. This is the number that decides whether you are labelled normal, osteopenic or osteoporotic.
• Your Z-score — how your bone density compares with other people of your own age and sex. This matters most in younger adults, where an unusually low Z-score suggests a second cause worth investigating.
• Change over time — if you have had a previous DXA scan on the same machine, the report will show whether your density has held, improved or fallen.

A DXA scan does not show cancer, arthritis, disc problems, soft tissue injuries or the cause of back pain. It measures mineral in bone and nothing else. See understanding your DXA results for what each score range means.

What to Expect on the Day

A DXA scan is straightforward and comfortable. Here is what typically happens:

1. Arrival: You check in at the radiology or bone density department. In public hospitals, this is usually as an outpatient.
2. Clothing: You will be asked to remove any metal-containing clothing or items from the scan area (such as belts, jewellery, or clothing with metal zips). In some cases, you may be given a gown. Loose, comfortable clothing without metal fastenings is ideal.
3. The scan: You lie flat on a padded scanning table. The scanner arm passes over your body — you do not go inside a tunnel (unlike an MRI). You need to remain still for a few minutes.
4. Hip scan: Your leg is positioned in a special brace to hold it at the correct angle. This is not painful.
5. Spine scan: A foam block is placed under your knees to flatten the lower spine against the table.
6. Duration: The full scan takes around 10–20 minutes including set-up time.
7. After the scan: You can leave immediately. There is no recovery time needed.

What Can Affect the Results?

Some factors can affect DXA scan accuracy or interpretation, including:

• Previous spinal fractures or severe spinal arthritis (can falsely elevate spine BMD readings)
• Hip replacements (that hip cannot be assessed)
• Very high or very low body weight
• Barium or contrast agents (if you have had certain medical tests recently)

The radiographer or reporting doctor will note these factors when interpreting your results.

Who Should Have a DXA Scan?

Your doctor may refer you for a DXA scan if you:

• Have had a fragility fracture (broken bone from a low-energy impact)
• Are a post-menopausal woman, particularly under 65 with additional risk factors
• Are a woman aged 65 or over
• Are a man aged 65 or over with risk factors
• Are on long-term oral corticosteroid therapy (such as prednisolone)
• Are receiving treatments that affect bone density (e.g., androgen deprivation therapy for prostate cancer, aromatase inhibitors for breast cancer)
• Have a medical condition associated with bone loss (e.g., coeliac disease, inflammatory bowel disease, hyperthyroidism)
• Have a FRAX score above certain intervention thresholds

Results and Follow-Up

Results are typically sent to your referring doctor within 1–2 weeks. Your doctor will explain the findings and discuss next steps. Results are given as a T-score (and sometimes a Z-score).

Learn more about what these scores mean on our Understanding Your Results page.

How Often Should You Have a DXA Scan?

Bone changes slowly, so scans are not repeated often. As a general guide in Irish practice:

• Normal result, low risk — a repeat is often not needed for several years, if at all
• Osteopenia — commonly repeated after roughly two years to see whether the trend is downward
• Starting or changing treatment — commonly repeated after one to two years to check the medication is working
• On long-term steroids or after a new fracture — your doctor may scan sooner

Repeating a scan more often than this rarely changes anything, because the real change in density over a single year is usually smaller than the scanner's own margin of error.