Bone Density Test (DEXA Scan) — How It Works, Benefits & Recovery — Procedure Guide, Recovery & Risks | MyMedicPlus

A bone density test — most commonly performed using dual-energy X-ray absorptiometry (DEXA or DXA) — measures bone mineral density (BMD) at the lumbar spine (L1–L4) and proximal femur (femoral neck and total hip). It is the WHO-endorsed gold-standard investigation for diagnosing osteoporosis, quantifying fracture risk, and monitoring response to anti-osteoporosis therapy. DEXA uses two X-ray beams of different energies; the differential absorption by bone and soft tissue generates a precise BMD measurement in g/cm². The result is expressed as a T-score (comparison to young adult peak BMD) and Z-score (age- and sex-matched comparison). Peripheral DEXA (forearm, heel) is a lower-cost screening option but central DEXA (spine and hip) is preferred for diagnosis and treatment decisions. A bone density test — most commonly performed using dual-energy X-ray absorptiometry (DEXA or DXA) — measures bone mineral density (BMD) at the lumbar spine (L1–L4) and proximal femur (femoral neck and total hip) and generates a T-score (comparison to a young adult reference population) and Z-score (comparison to age-matched peers). A T-score below −2.5 at either site diagnoses osteoporosis; between −1.0 and −2.5 indicates osteopenia. Osteoporosis affects approximately 200 million women and 20 million men globally, causing over 8.9 million fractures annually worldwide. DEXA scanning is performed by radiographers or radiological technologists on a dedicated low-dose X-ray scanning unit and interpreted by radiologists or endocrinologists. It is used both for initial diagnosis and for monitoring treatment response — repeated every 1–2 years depending on baseline BMD and treatment. FRAX (Fracture Risk Assessment Tool) incorporates BMD T-score with clinical risk factors to calculate a 10-year probability of major osteoporotic fracture to guide treatment thresholds.

NICE and WHO recommend DEXA scanning for: all women aged 65 and over; all men aged 70 and over; post-menopausal women under 65 with risk factors (prior fragility fracture, body weight under 58 kg, family history of hip fracture, smoking, excessive alcohol); men aged 50–70 with risk factors; patients on systemic glucocorticoids for 3 or more months; individuals with conditions causing secondary osteoporosis (rheumatoid arthritis, coeliac disease, hypogonadism, primary hyperparathyroidism); patients with a prior fragility fracture regardless of age; and patients being considered for anti-osteoporosis pharmacological therapy where BMD measurement influences prescribing decisions. The FRAX tool (WHO Fracture Risk Assessment) integrates DEXA results with clinical risk factors to calculate 10-year fracture probability. NICE guidelines and WHO recommendations support DEXA scanning for all women aged 65 and over, all men aged 70 and over, and post-menopausal women under 65 with risk factors including prior fragility fracture, family history of hip fracture, body mass index below 22 kg/m², early menopause (before age 45), prolonged glucocorticoid use (prednisolone 7.5 mg/day or more for 3 months or longer), or conditions associated with secondary osteoporosis such as rheumatoid arthritis, inflammatory bowel disease, and malabsorption syndromes. Men on androgen deprivation therapy for prostate cancer and patients on long-term aromatase inhibitor therapy for breast cancer should be scanned before treatment and annually thereafter. Serial DEXA is used to monitor treatment response in patients prescribed bisphosphonates, denosumab, or anabolic agents (teriparatide, romosozumab).

The patient lies fully clothed (without metal) on a padded scanning table. A motorised scanning arm passes slowly over the lumbar spine and proximal femur, emitting two low-energy X-ray beams. The process is entirely painless and non-invasive, producing no radiation sensation. Standard scan sites are L1–L4 spine (averaged) and femoral neck/total hip. In patients with severe spinal deformity, bilateral femoral scanning replaces the spine measurement. The test takes 10–30 minutes total including positioning. Vertebral fracture assessment (VFA) — a lateral spine image taken during the same session — screens for radiographically silent vertebral compression fractures that would change fracture risk classification. Lateral forearm scanning may also be performed in selected patients (hyperparathyroidism screening). The patient lies fully clothed (without metal) on a padded scanning table. A motorised scanning arm passes slowly over the lumbar spine and proximal femur, emitting two low-energy X-ray beams (at 70 and 140 kVp) that are differentially absorbed by bone mineral and soft tissue. Scan time is 5–10 minutes per site. The computer software automatically delineates the region of interest and calculates BMD in g/cm². A whole-body composition scan (measuring fat mass, lean mass, and bone mineral content) may be added with an additional 5-minute scan. Lateral vertebral assessment (VFA) identifies vertebral fractures in the thoracolumbar spine using a low-dose lateral image, adding 2–3 minutes. Patients with hip arthroplasty or severe scoliosis require modified scan sites or alternative imaging (quantitative CT). The report, including T-scores, Z-scores, and comparison to the patient's prior scans, is reviewed by the interpreting clinician.

DEXA provides the most accurate non-invasive measurement of BMD available, with precision errors of 1–2%. T-score results directly guide treatment decisions: T-score above −1.0 (normal) requires no pharmacological treatment; −1.0 to −2.5 (osteopenia) indicates lifestyle measures and monitoring; below −2.5 (osteoporosis) indicates bisphosphonate therapy (alendronate, risedronate, zoledronic acid) or denosumab. Initiating treatment after an abnormal DEXA result reduces vertebral fracture risk by 40–70% and hip fracture risk by 30–50% with bisphosphonates. Repeat DEXA at 1–2 years during therapy documents treatment response by monitoring BMD changes. Identifying osteoporosis before the first fracture prevents the morbidity and mortality associated with hip and vertebral fractures. DEXA provides the most accurate non-invasive measurement of BMD available, with precision errors of 1–2%. T-score results directly guide treatment decisions using established threshold criteria, preventing both under-treatment of at-risk patients and unnecessary medication in those with normal bone density. Detection and treatment of osteoporosis has been shown to reduce hip fracture risk by 30–50% with bisphosphonates and by 60–70% with denosumab. Serial DEXA monitoring tracks treatment effectiveness — patients showing adequate BMD gains over 2–3 years gain reassurance that therapy is working, while non-responders can switch to anabolic agents. FRAX integration makes the scan clinically actionable even at borderline T-scores. The test is widely available, quick (under 30 minutes), and requires no special preparation beyond removing metal items.

DEXA uses extremely low radiation doses (1–3 microsieverts per scan, approximately one-tenth of a chest X-ray or 3 hours of background radiation). There are no clinically significant radiation risks at these doses. The test is contraindicated during pregnancy as a precaution. Accuracy can be affected by: metal implants or dense calcifications in the scan field (overestimates BMD), vertebral fractures at scanned levels (overestimates spine BMD), and severe obesity (reduces soft-tissue correction accuracy). DEXA measures areal BMD (g/cm²) rather than true volumetric density, which slightly underestimates BMD in smaller-framed individuals — a limitation addressed by vertebral dimensions adjustment. DEXA uses extremely low radiation doses (1–3 microsieverts per scan, approximately one-tenth of a chest X-ray), making it safe for repeated monitoring over many years. There are no known health risks at diagnostic DEXA radiation levels. Artefacts from metal implants, calcium tablets, contrast media, or severe degenerative spine changes can falsely elevate lumbar spine BMD and must be reported to the operator beforehand. DEXA cannot assess bone microarchitecture or trabecular connectivity — limitations overcome by trabecular bone score (TBS) software or high-resolution peripheral quantitative CT (HR-pQCT) in research settings. False-positive results (normal T-score despite poor bone quality) can occur in severe osteoarthritis and Paget's disease, requiring clinical correlation. The test does not diagnose the cause of osteoporosis — secondary causes require additional blood tests including calcium, vitamin D, parathyroid hormone, and thyroid function.

No recovery is required after a DEXA scan. Patients resume all activities, including driving, immediately. Calcium supplements should not be taken on the day of the scan as they may affect scan accuracy in some protocols. Results are reported by a radiologist or clinical densitometrist as a T-score and Z-score, with interpretation and treatment recommendations provided in a structured report to the referring clinician. Results should be interpreted alongside clinical risk factors using the FRAX calculator. Follow-up DEXA scanning is recommended at 1–2 years after initiating pharmacological therapy to confirm treatment response, and every 3–5 years for monitoring in lower-risk individuals not on therapy. No recovery is required after a DEXA scan. Patients resume all activities, including driving, immediately after the test. Calcium supplements should not be taken on the day of the scan as they can affect scan accuracy; all other medications are taken as normal. The scan itself is completely painless and non-invasive — the patient simply lies still on the table while the scanning arm passes over them. Results are typically available within 1–7 days and are discussed with the referring physician at a follow-up appointment. Patients with T-scores indicating osteoporosis will be counselled on lifestyle measures (calcium and vitamin D optimisation, weight-bearing exercise, fall prevention) and initiated on pharmacological therapy as appropriate. The DEXA scan will be repeated at intervals determined by the clinical scenario — typically 2 years after starting treatment.