DXA Scan (Bone Density Test): What It Measures, What It Cannot, and How to Read Your Report

Key takeaways

• What DXA measures: bone mineral density at specific sites, reported as T-scores and Z-scores.
• What DXA does not do: it does not diagnose the cause of bone loss, does not assess bone quality, and a normal result does not mean a fracture cannot occur.
• Site matters: lumbar spine and hip are the standard sites; forearm is used when spine or hip cannot be measured reliably.
• Interpretation is contextual: the same T-score means different things in a 30-year-old man, a postmenopausal woman, and a person on long-term steroids.
• Comparability: follow-up scans are most meaningful when performed on the same machine, by the same protocol.

At a glance

Also known as

• DEXA scan / DXA scan
• Bone density test, BMD test
• Osteoporosis test, "bone scan for osteoporosis" (note: this is not the same as a nuclear medicine bone scan)
• Haddi ki density test / bone strength test, as commonly requested in Indian clinics

What a DXA scan is

The DXA scan passes two X-ray beams of different energies through a region of the body. Bone absorbs the two energies differently from soft tissue, and the machine uses that difference to calculate how much mineral is present per unit area of bone. This is reported as bone mineral density in g/cm? then converted into standardised scores.

Density is not the same as strength. Bone strength also depends on architecture, turnover, collagen quality and geometry, none of which a DXA scan measures directly. This is why two people with identical T-scores can have different fracture risks.

Why a DXA scan is done

• To support an osteoporosis diagnosis in postmenopausal women and men over 50, using T-scores.
• To help estimate fracture risk, usually combined with clinical risk factors rather than used alone.
• To monitor bone density over time in people on osteoporosis treatment or with ongoing bone loss risk.
• To assess bone in people on long-term glucocorticoids or other therapy associated with bone loss.
• To investigate unexplained low bone mass in younger adults, where Z-scores are used and secondary causes are sought.
• Body composition assessment on some machines, as a separate protocol from bone density.

Who should consider a DXA scan

Referral thresholds differ between guidelines and should be decided by your doctor. A DXA scan is commonly considered for:

• Postmenopausal women, particularly older postmenopausal women or those with additional risk factors such as early menopause, low body weight, smoking or a family history of hip fracture.
• Men in older age groups, or men with hypogonadism or other risk factors.
• Anyone who has had a fracture after minimal trauma (a fall from standing height or less).
• People on long-term glucocorticoids, aromatase inhibitors, androgen deprivation therapy, some antiepileptics, or long-term heparin, discuss timing with the prescriber.
• People with rheumatoid arthritis, inflammatory bowel disease, coeliac disease, chronic kidney disease, chronic liver disease, hyperparathyroidism, thyrotoxicosis, eating disorders, or after bariatric surgery.
• Women with prolonged amenorrhoea, and adults with height loss or a new stooped posture.
• Long-term post-transplant patients and people with HIV on certain regimens.

A DXA scan is generally not useful as a casual "health package" add-on in young, healthy adults with no risk factors, because the result rarely changes management and can cause unnecessary worry.

What a DXA scan cannot detect or exclude

• It does not explain why bone density is low. Vitamin D deficiency, coeliac disease, hyperparathyroidism, myeloma, thyroid disease and medication effects all need separate blood tests or investigations.
• A normal DXA does not exclude osteoporosis-related fracture risk. Many fragility fractures occur in people whose T-scores are above -2.5. Low bone density is one risk factor, not the whole picture.
• It does not diagnose a fracture. A standard DXA scan is not a fracture study. Suspected fracture needs X-ray, CT or MRI. Some units add vertebral fracture assessment (VFA) imaging, but this is a lower-resolution screen, not a substitute for spinal radiography.
• It does not assess bone quality, microarchitecture or turnover.
• It cannot distinguish osteoporosis from osteomalacia or from focal bone lesions.
• It does not diagnose bone cancer, metastases, infection or marrow disease.
• It does not measure cartilage, discs or joints, so it says nothing about arthritis or back pain.
• It is a two-dimensional (areal) measurement. Very small or very large body frames can shift the result, which limits its use as a standalone number, especially in children and in adults of short stature.

If your DXA scan is reported as normal but you still have bone pain, height loss, or a fracture after minor injury, return to your doctor. A normal result describes what was measured, not what has been excluded.

Related but different examinations

DXA and these tests answer different questions. None is universally superior; which comes first depends on the clinical problem. Someone with sudden severe back pain after a minor fall needs imaging for fracture first, not a density measurement. Someone being screened for silent bone loss needs DXA.

How to prepare

Preparation details, appointment lengths and device capability are operational matters that differ between units. Always follow the written instructions given by the centre performing your scan, those instructions take precedence over any general guidance here.

• Clothing: wear clothes without zips, hooks, metal buttons, underwired bras or belt buckles over the abdomen and hips. A gown may be provided.
• Jewellery and objects: remove abdominal piercings and empty pockets of coins, keys and phones.
• Recent scans: tell the unit if you have had a barium study, iodinated CT contrast, or a nuclear medicine scan in the preceding days, residual contrast or tracer can distort results, and the scan may need rescheduling.
• Calcium supplements: some units ask you not to take oral calcium on the morning of the scan, as undissolved tablets in the bowel can overlie the spine. Ask your unit; do not stop any prescribed medicine on your own.
• No fasting: a DXA scan does not normally require fasting or a special diet. Eat and drink as usual, and take your regular medicines as prescribed unless your unit or prescriber has told you otherwise.
• Bring prior reports: earlier DXA reports, including the machine details, help with meaningful comparison.
• Tell the unit about spinal implants, hip replacements, scoliosis, previous vertebral fractures, laminectomy or vertebroplasty. These affect which sites can be measured.

Pregnancy and possible pregnancy

Tell the staff before the scan if you are pregnant or think you might be. A DXA scan uses ionising radiation, and it is usually deferred in pregnancy unless there is a compelling reason and the referring doctor and radiologist have judged the benefit to outweigh the risk.

Breastfeeding

Breastfeeding is not affected by a DXA scan, as no radiotracer or contrast is given.

Children and adolescents

Paediatric DXA requires paediatric-specific software, age- and sex-matched reference data, and adjustment for body size and pubertal stage. Adult T-scores must not be applied to children, and "osteoporosis" in a child is not diagnosed on density alone. Ask whether the unit performs paediatric DXA before booking.

Older adults and people with limited mobility

Lying flat with legs positioned in a frame may be difficult with severe kyphosis, hip contractures or Parkinson's disease. Tell the unit in advance so staff can plan positioning and assistance. Severe spinal degeneration often makes hip or forearm the more reliable site.

Large body size

DXA tables have weight and width limits that vary by machine, and very large soft-tissue thickness can reduce accuracy. Confirm suitability with the unit beforehand.

Chronic kidney disease

In advanced CKD, low bone density may reflect renal osteodystrophy rather than postmenopausal osteoporosis, and treatment decisions differ. DXA still adds fracture-risk information, but interpretation must involve the nephrology team.

What happens during a DXA scan

There are no needles and no enclosed tunnel. You lie on your back on an open padded table while a scanning arm moves above you.

• Positioning: for the lumbar spine, your legs are raised on a foam block to flatten the lower back. For the hip, the leg is rotated inwards in a positioning brace.
• The scan: the arm passes slowly over each region while you lie still and breathe normally. You will not feel anything.
• Additional views: forearm scans or vertebral fracture assessment may be added if the referring doctor requested them or if the spine and hip are unmeasurable.
• Afterwards: no recovery period is needed. You can eat, drive and resume normal activity immediately.

How long does the process take

• Actual scanning: each site typically takes a few minutes; a standard spine-and-hip study usually falls within roughly 10-20 minutes including positioning.
• Total visit: allow additional time for registration, changing, and completing a risk-factor questionnaire.
• Reporting: report release times differ between units, ask the centre at the time of booking. Your own doctor then interprets the report alongside your history, medicines and risk factors.

Understanding your DXA report

The DXA report gives a bone mineral density value in g/cm?for each site, plus standardised scores. Do not treat a score as a diagnosis on its own.

T-score

The T-score compares your bone mineral density with the mean for a young adult reference population, expressed in standard deviations. Under the widely used WHO-based classification, a T-score of -1.0 or above is described as normal, between -1.0 and -2.5 as low bone mass (osteopenia), and -2.5 or below as osteoporosis. Standard practice applies these categories to postmenopausal women and to men aged 50 and over, at the lumbar spine, total hip or femoral neck. [Confirm current edition of the guideline your unit follows, TO BE VERIFIED]

The word "osteopenia" describes a measurement band, not a disease. Many people in that band never fracture, and treatment decisions in this range depend on overall fracture risk, not the number alone.

Z-score

The Z-score compares your density with people of the same age, sex and, where reference data allow, similar background. Z-scores rather than T-scores are used for premenopausal women, men under 50, and children. A low Z-score prompts a search for secondary causes such as endocrine disease, malabsorption, chronic inflammation or medication effects. In these groups the correct reporting term is "below the expected range for age", not "osteoporosis".

Why site-to-site differences occur

Spine and hip results often differ. Diagnosis is generally based on the lowest of the valid measured sites, but a spine value inflated by arthritis or calcification should be interpreted cautiously rather than taken at face value.

Repeat scans and least significant change

A small change between scans may be measurement noise rather than real bone change. Meaningful comparison needs the same machine and technique, and the report should ideally state the least significant change for that unit. A difference in g/cm?matters more than a difference in T-score when tracking treatment. Results vary depending on individual clinical circumstances.

When DXA results can be misleading

Falsely raised density (bone looks stronger than it is)

• Degenerative spinal disease, osteophytes, facet joint arthritis and endplate sclerosis, common in older adults, inflating lumbar spine values.
• Vertebral compression fracture within the scanned region.
• Aortic calcification overlying the lumbar spine.
• Spinal implants, surgical clips, vertebroplasty cement, or a hip prosthesis in the measured field.
• Residual oral contrast, undissolved calcium tablets, retained barium, or a recently injected radiotracer.
• Scoliosis and abnormal curvature causing overlapping structures.
• Metal fastenings, coins or jewellery left in the field.

Falsely lowered or misleadingly low readings

• Laminectomy or removal of posterior vertebral elements at a measured level.
• Incorrect vertebral labelling or inconsistent region-of-interest placement between visits.
• Very small body frame, where areal density under-reads true volumetric density.
• Comparison across different machines or manufacturers.

Other sources of misinterpretation

• Applying adult T-scores to children or young adults.
• Reporting a single site while ignoring artefacts at that site.
• Reference database differences, which affect T-score values, a concern where population-specific Indian reference data are limited.

If the report mentions degenerative change or artefact, ask your doctor which site should guide decisions.

Risks and safety

Standard central DXA (spine and hip)

The radiation dose from a standard DXA scan is low, considerably lower than a CT scan and comparable in magnitude to a small fraction of routine background exposure. There are no injections and no sedation. Very low risk is not the same as no risk, so the scan should be performed when there is a clinical reason for it.

Vertebral fracture assessment (VFA) add-on

VFA imaging adds a small amount of additional radiation. It provides a screening view of vertebral shape and is less detailed than a dedicated spinal X-ray.

Body composition scans

Body composition DXA uses a separate protocol with its own dose and its own reference data. Body composition values should not be read as bone diagnosis, and vice versa.

Peripheral devices and quantitative ultrasound

Heel ultrasound involves no ionising radiation but does not give a diagnostic T-score equivalent to central DXA. A reassuring peripheral result does not exclude osteoporosis at the spine or hip.

Pregnancy

Because ionising radiation is involved, DXA is generally deferred in pregnancy. Inform staff before the scan.

Special situations

Postmenopausal women

Bone loss accelerates after menopause, and T-score-based diagnosis applies in this group. Early or surgical menopause increases risk and may warrant earlier assessment.

Premenopausal women and men under 50

Z-scores are used. A low value is a prompt to investigate secondary causes rather than an automatic osteoporosis label.

Children and adolescents

Paediatric interpretation requires size- and maturity-adjusted reference data and should be done by a clinician experienced in paediatric bone health.

People on long-term glucocorticoids

Steroid-related fracture risk can rise before density falls much, so decisions are not based on T-score alone. Never alter a steroid dose yourself; discuss it with the prescriber.

Diabetes

In type 2 diabetes, fracture risk can be higher than the T-score suggests. The density number may understate risk in this group.

Chronic kidney disease

Bone disease in CKD is complex and may involve mineral and hormone disturbances. Biochemistry and nephrology input guide management alongside DXA.

Cancer therapy

Aromatase inhibitors in breast cancer and androgen deprivation therapy in prostate cancer are both linked with bone loss, and DXA monitoring is commonly arranged by the treating oncologist.

After bariatric or gastrointestinal surgery, and in malabsorption

Reduced absorption of calcium and vitamin D affects bone. Site selection can also be affected by body habitus changes.

DXA scanning in the Indian context

• Terminology: patients commonly ask for a "bone density test", "DEXA", or a "bone test for osteoporosis". Prescriptions may read "BMD DEXA spine and hip".
• Do not confuse machines: heel-based quantitative ultrasound units used at health camps and pharmacies are screening devices. If such a test suggests low bone mass, the appropriate next step is discussion with a doctor and, if indicated, a central DXA of spine and hip.
• Vitamin D and calcium intake: low vitamin D levels and low dietary calcium are widely reported in Indian populations across urban and rural settings. Because vitamin D deficiency can cause osteomalacia, which DXA cannot separate from osteoporosis, biochemical assessment often accompanies bone density testing.
• Reference data: T-scores depend on the reference database built into the machine. Indian population-specific normative data are limited, and this can shift T-score values. Ask your doctor which reference database was applied if a borderline result is driving a treatment decision.
• Coexisting conditions common in India: nutritional deficiency, thalassaemia and other haemoglobinopathies, long-term anti-tubercular therapy with associated vitamin D metabolism effects, chronic kidney disease, and prolonged corticosteroid use including unregulated steroid-containing preparations, all can affect bone and should be disclosed to your doctor.
• Regulatory note: promotional claims about bone "strengthening" products are governed by the Drugs and Magic Remedies (Objectionable Advertisements) Act, 1954. Be cautious of camp-based offers promising guaranteed improvement in bone density.
• Advertising and screening camps: a discounted bone test is not a substitute for clinical assessment. Bring any camp report to your doctor rather than starting supplements on your own.

Cost and insurance in India

DXA pricing in India varies widely between cities, between government and private facilities, and by the number of sites scanned. Any figure quoted online should be treated as indicative only; confirm the current price directly with the centre before booking. Factors that influence cost include:

• Number of regions scanned: spine only, spine plus hip, or a whole-body or body composition study.
• Add-on analyses such as vertebral fracture assessment or trabecular bone score, where available.
• Machine type: central DXA versus peripheral device.
• City and facility type: metro private hospital, standalone diagnostic centre, or government institution.
• Health-package bundling, which may include a bone test alongside other investigations.
• Consultation and interpretation fees, sometimes billed separately.
• Repeat monitoring scans, which are usually charged in full.

Insurance: outpatient diagnostic tests are often not covered under standard indemnity health insurance unless linked to an admission or covered by a specific OPD or wellness benefit. Coverage for investigation during an admission depends on policy terms and medical necessity. Check with your insurer or the hospital's insurance desk before the appointment. Government schemes and employee health schemes have their own rate lists and referral requirements.

Myths and facts

Frequently asked questions

Is a DXA scan the same as a bone scan?

No. A DXA scan measures bone mineral density using low-dose X-rays and involves no injection. A nuclear medicine bone scan uses an injected radiotracer to look for abnormal bone activity such as infection, metastasis or occult fracture. The two tests answer different questions and are not interchangeable.

How often should a DXA scan be repeated?

There is no single interval for everyone. Repeat timing depends on the initial result, the reason for testing, whether treatment has started, and ongoing risk factors. Because small changes may be measurement noise, scans are usually spaced out. Your doctor decides the interval, ideally using the same machine each time.

Can a DXA scan diagnose the cause of my bone loss?

No. The DXA scan quantifies density but cannot show why bone is weak. Blood tests for calcium, phosphate, vitamin D, parathyroid hormone, thyroid and kidney function, coeliac screening and myeloma investigation are used to look for secondary causes when the result is unexpectedly low.

Do I need to stop calcium tablets before the scan?

Some units ask you to skip oral calcium on the morning of the scan because undissolved tablets can overlie the spine. Follow the instruction your unit gives. Do not stop any prescribed medicine, including osteoporosis treatment, without speaking to your prescriber.

Which site is scanned, and why does my spine result differ from my hip?

The lumbar spine and hip are standard. Results often differ because arthritis, osteophytes, aortic calcification or previous fracture can falsely raise spine readings. Diagnosis generally uses the lowest valid site, with artefact-affected sites interpreted cautiously by the reporting doctor.

Can I have a DXA scan if I have a hip replacement or spinal implant?

Metal in the scanned field makes that region unmeasurable. The unit will usually scan the unoperated hip, an alternative site, or the forearm. Tell the centre about any implants when booking so appropriate sites are planned.

Is the radiation harmful if I need repeat scans?

The dose from a standard DXA scan is low relative to CT. Repeat scans at clinically appropriate intervals are considered reasonable, but scans are still performed only when there is a clinical reason. Tell staff if you are pregnant or might be, as the scan is usually deferred.

Will treatment definitely improve my T-score?

No outcome can be promised. Osteoporosis treatments aim primarily to reduce fracture risk, and density may improve, stabilise or change little. Results vary depending on individual clinical circumstances, adherence, nutrition and underlying conditions. Your doctor interprets follow-up scans against the expected measurement variation of the machine.

Can young adults or children have a DXA scan?

Yes, when clinically indicated, but interpretation differs. Z-scores are used rather than T-scores, and paediatric studies need size- and maturity-adjusted reference data. Adult osteoporosis criteria must not be applied. Confirm that the unit offers paediatric DXA reporting before booking.

Sources

• World Health Organization criteria for the diagnosis of osteoporosis based on bone mineral density measurement [Confirm current edition, TO BE VERIFIED]
• International Society for Clinical Densitometry (ISCD) Official Positions, Adult and Pediatric [Confirm current edition, TO BE VERIFIED]
• International Osteoporosis Foundation guidance on bone densitometry and fracture risk assessment [Confirm current edition, TO BE VERIFIED]
• Indian Society for Bone and Mineral Research (ISBMR) position statement on the diagnosis and management of osteoporosis in India [Confirm current edition, TO BE VERIFIED]
• Drugs and Magic Remedies (Objectionable Advertisements) Act, 1954, Government of India