DEXA Scan (Bone Density Test): What It Measures, What It Cannot, and How to Read Your T-Score

Key takeaways

• DEXA measures density, not strength. Bone mineral density is one part of bone health; bone quality and microarchitecture are not measured.
• T-scores classify, they do not predict individually. A normal T-score lowers but does not remove fracture risk, and many fragility fractures occur in people without osteoporotic T-scores.
• Site matters. Diagnosis in most adults rests on lumbar spine and hip measurements; forearm scans are used in specific situations.
• Body composition DEXA is a different study from bone densitometry, with different protocols and different interpretation.
• Results vary depending on individual clinical circumstances and must be read by the doctor who requested the scan, alongside your history, medicines and risk factors.

At a glance

Also known as

• Bone density test / BMD test
• DXA scan (the preferred technical abbreviation)
• Bone densitometry
• Osteoporosis test / "haddi ki density test" in common Indian usage
• Body composition DEXA (when used for fat and lean mass)

What a DEXA scan is

The DEXA scan passes two X-ray beams of different energies through the body. Bone and soft tissue absorb the two energies differently, and the scanner uses that difference to calculate bone mineral density in grams per square centimetre. Because the measurement is taken through a two-dimensional projection, DEXA reports areal density, not true volumetric density, which is one reason body size influences the result.

The scanner arm moves over you while you lie on a padded table. Nothing is injected, nothing enters the body, and the table does not enclose you.

Who should consider a DEXA scan

Referral is a clinical decision. A DEXA scan is commonly considered for:

• Postmenopausal women and men in older age groups, particularly where additional risk factors are present.
• Anyone with a fragility fracture: a fracture from a fall from standing height or less.
• People on long-term glucocorticoids (oral steroids), aromatase inhibitors or androgen deprivation therapy.
• Early menopause or surgical removal of ovaries, and men with hypogonadism.
• Chronic conditions affecting bone: rheumatoid arthritis, coeliac disease and other malabsorption, inflammatory bowel disease, chronic kidney disease, chronic liver disease, hyperparathyroidism, hyperthyroidism, previous bariatric surgery.
• People already on osteoporosis treatment, for monitoring at intervals decided by the treating doctor.
• Loss of height or a new stooped posture, which may suggest vertebral fracture and usually needs imaging in addition to DEXA.

Routine DEXA in young, healthy adults without risk factors is generally not useful, because the result rarely changes management.

Why a DEXA scan is done

• To diagnose osteoporosis or low bone mass before a fracture occurs.
• To contribute to fracture risk assessment, usually combined with clinical risk factors rather than used alone.
• To monitor change in bone density over time or on treatment, using the same machine wherever possible.
• To assess body composition in selected clinical and sports-medicine settings, a separate study from bone densitometry.

What a DEXA scan cannot detect or exclude

This is the part most reports do not spell out.

• It does not measure bone strength or quality. Collagen structure, microarchitecture, bone turnover and mineralisation defects are invisible to DEXA. Two people with the same T-score can have different real-world fracture risk.
• A normal T-score does not exclude future fracture. A large share of fragility fractures occur in people whose T-scores fall in the osteopenic or normal range. If you have fractured easily, a normal DEXA does not overturn that fact, go back to your doctor.
• It is not a fracture-detection test. Standard bone densitometry is not designed to diagnose an acute fracture. Vertebral fracture assessment (VFA) is an add-on lateral spine image available on many scanners, but it is lower resolution than X-ray, and suspected fractures generally need dedicated radiographs, CT or MRI.
• It does not identify the cause of bone loss. Vitamin D deficiency, coeliac disease, myeloma, hyperparathyroidism, thyroid disease and drug effects require blood tests and clinical assessment, not DEXA.
• It does not diagnose osteomalacia, which is a mineralisation disorder and can coexist with low density.
• It does not assess bone pain or back pain. A DEXA scan will not explain why your back hurts.
• Body composition DEXA does not diagnose metabolic disease. A visceral fat estimate is not a substitute for blood pressure, glucose, HbA1c and lipid testing.
• Osteoarthritis, cancer, or spinal disc disease are not assessed by a bone density study.

"Not identified on DEXA" means it was not seen on this study, not that it does not exist. If symptoms persist despite a normal or reassuring result, return to your doctor.

Related but different examinations, and how they compare

These tests answer different questions. None is universally superior; the right first test depends on the clinical problem.

A heel ultrasound at a health camp suggesting "low bone density" is a prompt to see a doctor, not a diagnosis of osteoporosis.

How to prepare

Preparation rules are operational and vary between units and scanner manufacturers. Your imaging unit's instructions take precedence over anything written here.

• No fasting is needed for a bone density scan. Eat and drink normally unless your unit says otherwise.
• Calcium supplements are commonly withheld on the day of the scan, or for around 24 hours, because tablets in the gut can overlie the spine. Do not stop any prescribed medicine on your own, ask the prescriber or the imaging unit.
• Clothing: wear loose clothes without metal zips, hooks, buttons, underwiring or studs. Leave jewellery at home where possible. You may be given a gown.
• Recent contrast or barium: tell the unit if you have had a barium study, CT with contrast, or a nuclear medicine scan in the preceding days or weeks, these can invalidate the measurement, and the scan is usually rescheduled.
• Previous scans: bring earlier DEXA reports and images. Comparison is most reliable on the same machine.
• Declare implants and surgery: hip replacements, spinal rods, screws, plates, pacemakers and pumps in the scan field change which sites can be measured.
• Weight and table limits vary by scanner. Very large body habitus may exceed the table limit or the scan field; the unit can advise on alternatives.

If you are or might be pregnant

Tell the team before the scan. DEXA uses ionising radiation, and bone densitometry is generally deferred until after pregnancy unless there is a compelling clinical reason. Note also that in India, the PC-PNDT Act 1994 governs prenatal diagnostic procedures and sex determination; a DEXA scan is not a prenatal test and must never be used for any such purpose.

Children and adolescents

Paediatric DEXA is a specialist study. T-scores are not used in children; results are reported as Z-scores and adjusted for height or bone age by a paediatric endocrinologist or specialist radiologist. Reporting a child's result against adult standards leads to false alarm.

Older adults and people with limited mobility

Lying flat and still for the scan can be uncomfortable with severe kyphosis, hip pain or tremor. Tell the radiographer, positioning aids and shorter protocols can often help.

Chronic kidney disease

Bone disease in advanced CKD (renal osteodystrophy) is complex. DEXA can still be informative about fracture risk, but a T-score alone cannot distinguish the underlying bone disorder, and management differs from ordinary postmenopausal osteoporosis. Interpretation should involve the nephrology team.

What happens during the scan

• Check-in and screening: height and weight are measured, and you are asked about pregnancy, implants, fractures, recent contrast and medicines.
• Positioning: you lie on your back on a padded table. For the hip, the leg is rotated inward and held with a foam brace. For the spine, the legs are usually raised on a padded box to flatten the lower back.
• Scanning: the arm passes slowly over you. You breathe normally and stay still. Nothing touches you and there is no noise beyond a quiet motor.
• Duration: spine and hip acquisitions commonly take around 10-20 minutes in total including positioning. A whole-body composition scan usually takes longer. Older scanners are slower than modern ones.
• Afterwards: you can eat, drive and return to normal activity immediately. There is no residual radioactivity and nothing to avoid.

Understanding your report

T-score

The T-score compares your bone mineral density with that of a healthy young adult reference population. The World Health Organization classification, applied to postmenopausal women and men aged 50 and over at the lumbar spine, femoral neck or total hip, is:

• Normal: T-score of -1.0 or above
• Low bone mass (osteopenia): T-score between -1.0 and -2.5
• Osteoporosis: T-score of -2.5 or below

These are classification thresholds for populations, not individual verdicts. They are cut-offs on a continuous scale, a T-score of -2.4 and one of -2.6 are clinically almost identical, despite falling either side of a label.

Z-score

The Z-score compares your density with people of the same age, sex and often ethnicity. The Z-score is the appropriate report for premenopausal women, men under 50, and children. A low Z-score prompts a search for a secondary cause of bone loss rather than assuming age-related change. The WHO T-score categories should not be applied to these groups.

Absolute density and change over time

The report also gives density in g/cm? When comparing with a previous scan, what matters is whether the change exceeds the "least significant change" for that machine and technologist, small differences are often measurement noise, not real bone loss or gain. Comparisons between different machines or centres are unreliable.

Fracture risk tools

Many reports include a FRAX or similar fracture-risk estimate, which combines clinical risk factors with femoral neck density. These tools give population-level probabilities and depend on country-specific calibration and honest risk-factor entry. They inform treatment discussions; they do not predict what will happen to you.

Body composition results

Fat mass, lean mass, regional distribution and an estimated visceral adipose tissue value may be reported. Reference data differ between manufacturers and software versions, and there are no universally agreed clinical thresholds for many of these measures. Interpretation belongs with the clinician or sports physician who requested the study.

No DEXA report, on its own, is a diagnosis. Results require interpretation in clinical context by the doctor who requested the test.

When DEXA results can be misleading

Factors that can falsely raise bone density

• Degenerative spinal arthritis and osteophytes: very common after middle age, and a leading reason a lumbar spine reading looks better than the hip.
• Aortic calcification overlying the lumbar spine.
• Vertebral compression fractures, which paradoxically increase measured density in the collapsed vertebra; such vertebrae are usually excluded from the average.
• Spinal surgery, metalwork, cement or laminectomy within the scan field.
• Residual barium, contrast or radiopharmaceutical from a recent study.
• Calcium tablets in the gut, gallstones, renal stones or calcified lymph nodes projecting over the spine.
• Larger body size, because areal density does not fully correct for bone size, a factor that can flatter measurements in taller, heavier people.

Factors that can falsely lower bone density

• Small body frame or short stature, relevant for many South Asian patients, since areal density tends to under-read in smaller bones.
• Poor positioning or rotation of the hip, or inconsistent vertebral labelling between scans.
• Laminectomy removing posterior bone from the region of interest.
• Movement during acquisition.

Reference-database and comparison problems

• Ethnicity-specific normative data for Indian populations are limited, and the reference database selected by the operator changes the T-score.
• Different manufacturers (GE, Hologic, others) are not directly interchangeable; serial scans should be done on the same machine where possible.
• Software upgrades can shift values slightly between visits.
• Scanning too soon after a previous scan often produces a change smaller than the measurement error, which is uninformative.

Risks and safety

Standard bone densitometry (spine and hip)

The radiation dose is very low, typically a small fraction of a chest CT and comparable to a fraction of the natural background radiation everyone receives each year. It is low, not zero. The scan is non-invasive, requires no injection and causes no pain. There is no recovery period.

Whole-body composition DEXA

Whole-body acquisition scans a larger area and takes longer. Dose remains low but the study is not medically indicated for most people, and repeating it frequently for fitness tracking means repeated, unnecessary radiation exposure without clinical benefit.

Vertebral fracture assessment

VFA adds a lateral spine image and a small additional dose, still well below that of conventional spinal radiographs.

Pregnancy

DEXA is generally avoided in pregnancy because of foetal radiation exposure, and is usually postponed. Always declare a possible pregnancy.

Results and risk vary depending on individual clinical circumstances.

Special situations

Premenopausal women and men under 50

Z-scores, not T-scores, apply. A Z-score of -2.0 or below is described as "below the expected range for age" and prompts investigation for secondary causes. Osteoporosis is not diagnosed on density alone in these groups.

People on long-term steroids

Glucocorticoids increase fracture risk at higher density levels than usual, so treatment decisions may be made at T-scores that would otherwise be considered mild. Discuss timing of scans with the prescriber. Never stop or alter steroid therapy yourself.

People with hip replacement or spinal metalwork

The affected site cannot be measured. The opposite hip or the forearm (33% radius) is used instead. Tell the unit in advance so the correct protocol is selected.

People with diabetes

In type 2 diabetes, fracture risk can be higher than the T-score suggests, so a "reassuring" DEXA result should be interpreted cautiously alongside clinical risk. No fasting is required for a DEXA scan, so glucose-lowering medicines and meals continue as normal unless a different test is being done on the same visit, check with the prescriber if you are unsure.

Older adults with previous fracture

A prior fragility fracture is itself a strong risk factor and may justify treatment regardless of the T-score. The scan then serves mainly as a baseline for monitoring.

DEXA scanning in the Indian context

• Vitamin D deficiency is widely reported across Indian populations, including in sunny regions, and often coexists with low dietary calcium intake. Correcting deficiency is usually addressed before or alongside osteoporosis treatment, because treating with certain bone medicines in uncorrected deficiency can cause low calcium.
• Smaller average body and bone size in many South Asians can pull areal density measurements down, which is one reason results must be read with clinical judgement rather than by threshold alone.
• Reference databases used in Indian DEXA units are often derived from Western populations; the database applied affects the T-score, and this should be noted when comparing reports from different centres.
• Vegetarian diets, low dairy intake in some regions, and limited sun exposure from indoor work or full-coverage clothing are common contributors discussed in Indian practice.
• Long-term anti-tubercular therapy, anticonvulsants and corticosteroids are frequently encountered drug-related contributors to bone loss and should be declared at referral.
• Heel ultrasound screening at camps and pharmacies is widespread. It may identify people who should be assessed further, but it does not diagnose osteoporosis and should not be used to start treatment.
• Regulatory note: DEXA involves ionising radiation and equipment is regulated under India's atomic energy radiation safety framework. The PC-PNDT Act 1994 applies to prenatal diagnostic procedures, DEXA has no role there. Any online enquiry or booking form collecting your health data is governed by the Digital Personal Data Protection Act 2023.

Cost and insurance in India

Prices differ widely across cities, hospital categories and scanner types. Treat any figure you see online as indicative only; confirm the current price with the facility before booking.

Factors that influence what you pay:

• Number and choice of sites: spine only, spine and hip, forearm, or whole body.
• Whole-body composition studies, which are usually priced separately and higher than a two-site bone scan.
• Add-ons such as vertebral fracture assessment or formal fracture-risk reporting.
• City and facility type: metro tertiary hospitals generally cost more than standalone diagnostic centres.
• Scanner generation and accreditation of the laboratory.
• Bundling within osteoporosis or executive health packages, often with blood tests included.
• Consultation and reporting fees, which may or may not be included.

Insurance: outpatient diagnostic tests are frequently not covered under standard indemnity health insurance policies in India unless linked to an admission or covered by an OPD rider or a corporate health scheme. Where a DEXA scan forms part of an inpatient work-up, it is more likely to be reimbursed. Check with your insurer or the hospital's TPA desk before the scan.

Myths and facts

Frequently asked questions

How long does a DEXA scan take?

A standard spine and hip DEXA usually takes about 10-20 minutes from lying down to finishing, including positioning. Whole-body composition scans generally take longer. Actual times depend on the scanner generation and the number of sites requested, so allow extra time for registration and screening questions.

Do I need to fast before a DEXA scan?

No. Bone densitometry does not require fasting, and you can eat, drink and take your usual food normally. Many units ask you to skip calcium supplements on the day, because undissolved tablets in the gut can overlie the spine. Follow your own unit's written instructions.

Does a DEXA scan hurt?

No. Nothing is injected and nothing touches you. You lie on a padded table while the scanner arm passes overhead. The main discomfort reported is lying still on a firm surface, which can be difficult with severe back or hip pain. Tell the radiographer if positioning is painful.

How often should a DEXA scan be repeated?

Repeat intervals are individual and decided by your doctor. Scanning too soon often shows changes smaller than the machine's measurement error, which is uninformative. Intervals are typically longer for low-risk people and shorter when treatment response or rapid bone loss is being monitored. Use the same scanner for comparison where possible.

Is a DEXA scan safe during pregnancy?

DEXA uses ionising radiation, so bone densitometry is generally postponed during pregnancy. Tell the imaging team before the scan if you are pregnant or might be. If bone assessment is genuinely urgent, your doctor will weigh alternatives and timing with you.

Can a DEXA scan detect a broken bone?

Not reliably. Standard densitometry is not a fracture-detection study. Some scanners offer vertebral fracture assessment, which can suggest existing vertebral collapse, but it has lower image detail than X-ray. Suspected fractures generally need dedicated radiographs, CT or MRI.

Is DEXA body composition better than a bioimpedance body fat machine?

DEXA generally provides more detailed regional fat and lean mass data than bioimpedance scales, which are sensitive to hydration and recent meals. However, DEXA involves radiation, is costlier, and its visceral fat values are estimates that differ between manufacturers. Neither test diagnoses disease on its own.

My T-score is -2.6. Do I have to start medication?

Not automatically. A T-score of -2.6 meets the classification for osteoporosis, but treatment decisions also consider your age, fracture history, steroid use, vitamin D status, falls risk and other conditions. Discuss options with your doctor, and do not start or stop any medicine without their advice.

Why is my spine result better than my hip result?

This pattern is common after middle age. Degenerative arthritis, osteophytes, aortic calcification, scoliosis or previous vertebral collapse can artificially raise lumbar spine density. When the spine is unreliable, the reporting doctor generally gives more weight to the hip measurement.

Sources

• World Health Organization, diagnostic criteria for osteoporosis based on bone mineral density T-scores.
• International Society for Clinical Densitometry (ISCD), Official Positions on DXA acquisition, site selection, Z-score use in premenopausal women, men under 50 and children, and least significant change.
• International Osteoporosis Foundation, FRAX fracture risk assessment and country-specific calibration.
• Royal Osteoporosis Society and NICE guidance on osteoporosis risk assessment and bone density testing.
• Indian Menopause Society and Indian Society for Bone and Mineral Research guidance on osteoporosis management in India.
• Published Indian literature on vitamin D deficiency prevalence and bone mineral density reference data in Indian populations.