How to Interpret Your DEXA Bone Density Result

What the DEXA Scan Actually Measures

A DEXA (dual-energy X-ray absorptiometry) scan uses two low-dose X-ray beams at different energy levels to estimate grams of mineral per square centimeter of bone. The result is your bone mineral density, reported in g/cm². That raw number is then converted into two standardized scores that clinicians use to classify fracture risk.

The International Society for Clinical Densitometry (ISCD) considers the posteroanterior lumbar spine (L1-L4) and the proximal femur the primary diagnostic sites in most adults. The ISCD 2019 Official Positions state that the lowest T-score from either the spine, total hip, or femoral neck should be used for diagnosis.

T-Score: What It Compares

The T-score expresses your BMD as a number of standard deviations above or below the mean BMD of a healthy young adult reference population (peak bone mass, typically ages 20-29). A T-score of -1.0 means your BMD is one standard deviation below that peak. Each standard deviation corresponds to roughly a 10-12% difference in BMD and approximately a doubling of fracture risk, according to data from the Study of Osteoporotic Fractures (pubmed.ncbi.nlm.nih.gov/1439480).

The WHO diagnostic categories, confirmed in the 2020 AACE/ACE Clinical Practice Guidelines for the Diagnosis and Treatment of Postmenopausal Osteoporosis, are:

| Category | T-score | |---|---| | Normal | -1.0 and above | | Osteopenia (low bone mass) | Below -1.0 to -2.5 | | Osteoporosis | -2.5 and below | | Severe osteoporosis | -2.5 and below plus fragility fracture |

Z-Score: What It Compares

The Z-score compares your BMD to an age-, sex-, and ethnicity-matched reference group. A Z-score of -2.0 or lower is defined as "below the expected range for age" by the ISCD (pubmed.ncbi.nlm.nih.gov/31421109). In premenopausal women, men under 50, and children, the Z-score is the preferred diagnostic metric because the T-score is not validated in those groups.

A Z-score below -2.0 should prompt evaluation for secondary causes of bone loss: glucocorticoid use, hyperparathyroidism, celiac disease, or hypogonadism, among others. The Endocrine Society's 2012 clinical practice guideline on male osteoporosis recommends secondary workup whenever the Z-score falls at or below -2.0 in men.

Understanding the WHO Diagnostic Thresholds

The WHO thresholds were established in a 1994 technical report (WHO Technical Report Series 843) using data from Caucasian women. They have since been validated across broader populations, though with some limitations in men and non-Caucasian groups. The National Osteoporosis Foundation (NOF) and AACE apply these thresholds to postmenopausal women and men aged 50 and older.

Osteopenia is not a disease. It is a statistical descriptor indicating BMD below peak but not yet at the fracture-risk threshold that defines osteoporosis. Many people with osteopenia never fracture. Conversely, because osteopenia is far more prevalent than osteoporosis, the FRAX data published in Osteoporosis International show that a majority of osteoporotic fractures actually occur in people with T-scores in the osteopenic range, simply because more people fall in that category.

Why Site Selection Matters

Lumbar spine BMD tends to decrease first in early menopause. Hip BMD is the stronger predictor of hip fracture risk. The Study of Osteoporotic Fractures (N=9,516) demonstrated that femoral neck BMD predicted hip fracture better than spine BMD in older women. For that reason, the femoral neck T-score is used as the primary input for FRAX calculations.

Spinal degenerative disease, aortic calcification, and vertebral fractures can all artificially raise spine BMD, making the spine score falsely reassuring in older adults. When this is suspected, clinicians may rely primarily on hip measurements.

Serial Scans and Least Significant Change

A single T-score is a snapshot. When monitoring over time, the change in BMD must exceed the machine's precision error to be considered real. Most DXA systems have a least significant change (LSC) of approximately 3-5% at the spine and hip. The ISCD 2019 Official Positions require each facility to calculate its own LSC rather than using published averages. A 2% change on your report does not necessarily mean your bones have actually changed.

How to Use the FRAX Score Alongside Your T-Score

The T-score alone does not determine whether you need medication. The FRAX tool, developed by the WHO Collaborating Centre at Sheffield and validated in the FRAX cohort analysis (Kanis et al., Osteoporosis International, 2008), calculates your 10-year probability of hip fracture and major osteoporotic fracture (hip, spine, forearm, or shoulder) using up to 12 clinical risk factors.

FRAX inputs include age, sex, body mass index, prior fragility fracture, parental hip fracture history, current smoking, glucocorticoid use, rheumatoid arthritis, secondary osteoporosis causes, and alcohol intake of three or more units per day. Femoral neck T-score is optional but improves accuracy when available.

Treatment Thresholds in Major Guidelines

The 2020 AACE/ACE guidelines classify postmenopausal osteoporosis risk as follows:

• Low risk: T-score above -1.0, no prior fracture, low FRAX probability
• Moderate risk: T-score between -1.0 and -2.0 or 10-year major fracture risk 10-20%
• High risk: T-score at or below -2.5, or prior fragility fracture, or 10-year major fracture risk above 20%
• Very high risk: T-score at or below -3.0, multiple fractures, or fracture on approved therapy

The NOF treatment threshold, as published in the 2014 Clinician's Guide to Prevention and Treatment of Osteoporosis, recommends pharmacotherapy when the 10-year probability of hip fracture reaches 3% or higher, or when the 10-year probability of major osteoporotic fracture reaches 20% or higher, even with a T-score in the osteopenic range.

USPSTF Screening Recommendations

The USPSTF 2018 recommendation statement on osteoporosis screening gives a Grade B recommendation for screening all women aged 65 and older, and for postmenopausal women younger than 65 whose 10-year fracture risk equals or exceeds that of a 65-year-old Caucasian woman (approximately 9.3% on the FRAX tool without BMD). The USPSTF found insufficient evidence to recommend routine screening in men.

What Raises Bone Density

Bone density can increase with targeted interventions. The FLEX trial (N=1,099) and the FIT trial (N=2,027) established that bisphosphonate therapy produces measurable BMD gains and fracture risk reduction.

Pharmacologic Options

Alendronate (70 mg once weekly orally) is the most widely prescribed first-line agent for osteoporosis. In the Fracture Intervention Trial (FIT), alendronate reduced vertebral fracture risk by 47% (relative risk 0.53, 95% CI 0.41-0.68) over 3 years in postmenopausal women with a prior vertebral fracture. Hip fracture risk fell by 51% in the subgroup with femoral neck T-scores at or below -2.5.

Risedronate (35 mg weekly) showed similar vertebral fracture reduction in the VERT-MN trial (N=1,226). Zoledronic acid (5 mg IV annually) reduced hip fracture risk by 41% in the HORIZON-PFT trial (N=7,736).

For very high-risk patients, anabolic agents offer greater BMD gains. Teriparatide (20 mcg subcutaneous daily) increased lumbar spine BMD by 9.7% and femoral neck BMD by 2.6% over 18 months in the Neer et al. NEJM trial (N=1,637). Romosozumab (210 mg subcutaneous monthly for 12 months) produced lumbar spine BMD gains of 13.3% in the ARCH trial (N=4,093) before transitioning to antiresorptive therapy.

Denosumab (60 mg subcutaneous every 6 months) reduced vertebral fracture risk by 68% and hip fracture risk by 40% in the FREEDOM trial (N=7,808) over 36 months.

Lifestyle Interventions

Weight-bearing and resistance exercise preserve BMD. A Cochrane review of exercise interventions for postmenopausal women (Howe et al., 2011) found that combined exercise programs reduced femoral neck bone loss. The effect sizes were modest (0.5-1.0% per year), but fracture risk reduction may exceed what BMD gains alone suggest because muscle strengthening also reduces fall risk.

Calcium and vitamin D supplementation supports bone remodeling. The Endocrine Society's 2011 vitamin D guideline recommends 1,500-2,000 IU/day of vitamin D3 for adults at risk for deficiency, with a target serum 25-hydroxyvitamin D of at least 30 ng/mL. Dietary calcium intake of 1,000-1,200 mg/day is recommended for postmenopausal women by the National Academies of Medicine (2011 DRI report).

What Lowers Bone Density

Several modifiable and non-modifiable factors accelerate bone loss.

Medications That Reduce BMD

Oral glucocorticoids are the most common drug-related cause of osteoporosis. The ACR 2017 Guideline for the Prevention and Treatment of Glucocorticoid-Induced Osteoporosis recommends baseline DEXA for any patient expected to take prednisone equivalent doses of at least 2.5 mg/day for 3 months or longer. Aromatase inhibitors used in breast cancer treatment lower estrogen to near-zero levels and produce lumbar spine BMD losses averaging 2-3% per year, as documented in the ATAC trial bone substudy. Androgen deprivation therapy (ADT) for prostate cancer lowers testosterone to castrate levels and may reduce hip BMD by 2-3% annually, per data from the Shahinian et al. NEJM analysis.

Proton pump inhibitors (PPIs) taken long-term have been associated with modestly increased fracture risk in observational studies. The FDA drug safety communication on PPI fracture risk notes a potential 10-40% relative risk increase with high-dose or long-duration use.

Hormonal and Metabolic Drivers

Estrogen deficiency is the primary driver of postmenopausal bone loss, with rates reaching 2-5% per year in the first 5 years after menopause. The WHI clinical trial showed that combined estrogen plus progestin reduced hip fracture risk by 33% (hazard ratio 0.67, 95% CI 0.47-0.96) over a mean follow-up of 5.6 years.

Testosterone deficiency in men produces parallel bone loss. The Testosterone Trials (TTrials) bone substudy (N=211) found that testosterone treatment in men aged 65 and older with low testosterone (<275 ng/dL) increased volumetric BMD by 7.5% at the trabecular spine and 3.7% at the femoral neck over 12 months (P<0.001).

Hyperthyroidism, primary hyperparathyroidism, and type 1 diabetes mellitus all independently reduce BMD through distinct mechanisms. Secondary workup with labs including thyroid-stimulating hormone, parathyroid hormone, serum calcium, 25-hydroxyvitamin D, and complete metabolic panel is appropriate whenever BMD loss exceeds what the clinical picture predicts.

Smoking and Alcohol

Smoking accelerates bone resorption through direct toxic effects on osteoblasts and indirect antiestrogenic effects. Current smokers have BMD approximately 0.1 standard deviations lower than non-smokers, and their fracture risk is elevated by roughly 25%, per meta-analysis data from Law and Hackshaw (BMJ, 1997).

Alcohol intake above two units per day is associated with reduced BMD and impaired fracture healing. The FRAX algorithm treats alcohol use above three units per day as an independent risk factor (Kanis et al., Osteoporosis International, 2005).

Normal DEXA Bone Density Ranges and How to Read Your Report

Your DEXA report will list BMD values in g/cm², T-scores, and Z-scores for each measured site. Most reports also print the WHO diagnostic category.

Reading the Spine Section

The lumbar spine section reports individual vertebral levels (L1, L2, L3, L4) and a composite L1-L4 score. The ISCD recommends excluding a vertebral level from the composite if its T-score differs from an adjacent level by more than 1.0 standard deviation, because local degenerative changes or fracture may distort that value. Your report may flag excluded levels.

Reading the Hip Section

The hip section typically shows total hip and femoral neck T-scores separately. Only the femoral neck T-score is used in FRAX calculations. The total hip T-score carries weight in monitoring BMD changes over time because it has a larger bone area and lower precision error than the femoral neck alone.

Forearm Measurements

The one-third (33%) radius site is measured when the spine and hip are unmeasurable or unreliable (severe obesity, bilateral hip arthroplasty), or in patients with primary hyperparathyroidism, where cortical bone loss may exceed trabecular bone loss. The ISCD 2019 positions specify the one-third radius as the diagnostic forearm site.

The HealthRX clinical team uses a four-step interpretation framework for every DEXA result reviewed on our platform:

Step 1. Identify the lowest T-score across spine, total hip, and femoral neck. Apply WHO categories.

Step 2. Check the Z-score. If it is -2.0 or lower, flag for secondary cause workup before attributing bone loss to age or menopause alone.

Step 3. Enter FRAX with and without BMD to calculate 10-year fracture probabilities. Use the country-specific FRAX model.

Step 4. Apply the AACE risk stratification (low/moderate/high/very high) to select a pharmacotherapy tier, if warranted. For patients already on therapy, compare current BMD to the prior scan using the facility-specific LSC to determine whether the response is adequate.

When to Repeat Your DEXA Scan

Repeat scan timing depends on baseline T-score and clinical context. The ISCD 2019 Official Positions provide the following guidance:

• Patients on pharmacotherapy: repeat at 1-2 years to assess treatment response
• Patients with osteopenia not on therapy: repeat every 2-5 years depending on baseline T-score severity
• Patients with normal BMD and no major risk factors: repeat every 10-15 years, or when new risk factors emerge
• Patients on long-term glucocorticoids: repeat annually for the first 2 years

The FLEX trial demonstrated that after 5 years of alendronate therapy, patients with femoral neck T-scores above -2.5 at year 5 could safely discontinue ("drug holiday") with acceptable fracture outcomes, while those with T-scores at or below -2.5 benefited from continued therapy. Serial DEXA results drive these drug holiday decisions.

Special Populations

Men

Osteoporosis in men is under-diagnosed. The IOF/ECTS 2012 guideline estimates that men account for approximately 30% of all osteoporotic fractures globally, with higher post-fracture mortality than women. FRAX can be applied to men aged 50 and older using the same WHO T-score thresholds.

Premenopausal Women

The WHO T-score thresholds do not apply to premenopausal women. The ISCD uses Z-scores exclusively in this group. A Z-score at or below -2.0 plus a low-trauma fracture supports a diagnosis of osteoporosis. The Endocrine Society guideline on premenopausal osteoporosis emphasizes ruling out secondary causes before initiating pharmacotherapy.

Patients on GLP-1 Receptor Agonists

Rapid weight loss, including from GLP-1 receptor agonist therapy such as semaglutide or tirzepatide, may reduce BMD. In the STEP-1 trial (N=1,961), semaglutide 2.4 mg produced 14.9% mean weight loss at 68 weeks versus 2.4% with placebo. Fat mass loss is generally protective for bone, but lean mass loss is not. Clinicians managing patients on high-dose GLP-1 therapy for longer than 12 months may consider baseline and follow-up DEXA, particularly in women over 45 or men over 55.

Patients on Testosterone or Estrogen Therapy

As noted above, testosterone therapy increases BMD in hypogonadal men. In postmenopausal women initiating hormone therapy for symptomatic menopause, DEXA is not required before starting but provides a useful baseline when osteoporosis risk is elevated. The Menopause Society (formerly NAMS) 2022 hormone therapy position statement acknowledges BMD preservation as a non-primary but clinically relevant benefit of systemic hormone therapy.