Bone Density Drugs That Distort Your DEXA Scan: A Clinical Guide

What a DEXA Bone Density Test Actually Measures

A DEXA scan uses two low-energy X-ray beams to estimate grams of mineral per square centimeter of bone (g/cm²) at the lumbar spine (L1-L4), total hip, and femoral neck. The raw g/cm² value is then converted to a T-score by comparing it to the average peak bone mass of a young-adult reference population. The Z-score compares results to age- and sex-matched peers instead. The WHO defines osteoporosis as a T-score at or below -2.5 at any of these three standard sites.

T-Score vs. Z-Score: Which One Matters

For postmenopausal women and men over 50, the T-score drives fracture-risk decisions. For premenopausal women, men under 50, and children, the Z-score is the appropriate metric because comparing a 35-year-old's bone to a 25-year-old reference peak is clinically misleading. The International Society for Clinical Densitometry (ISCD) published official positions on this distinction, referenced in the AACE 2020 osteoporosis guidelines.

What the Scan Cannot Tell You

DEXA measures density, not architecture. A vertebra can have a high BMD reading because of osteophytes, aortic calcification, overlying hardware, or compressed fracture fragments, all of which add mineral mass to the measurement region without making the bone stronger. This limitation becomes clinically significant when interpreting results in patients taking drugs that deposit mineral rapidly or alter trabecular microstructure.

Normal Ranges at a Glance

According to the WHO classification, adopted by the USPSTF in its 2018 recommendation statement on osteoporosis screening, the ranges are:

• T-score above -1.0: normal bone density
• T-score -1.0 to -2.5: osteopenia (low bone mass)
• T-score at or below -2.5: osteoporosis
• T-score at or below -2.5 plus a fragility fracture: severe osteoporosis

A Z-score at or below -2.0 in a premenopausal woman triggers the label "below the expected range for age" and prompts a secondary-cause workup.

Drugs That Artificially Raise DEXA Scores

Some medications increase the number the scanner reports without proportionally reducing fracture risk or, in some cases, even while bone quality deteriorates.

Bisphosphonates: The Artifact Problem

Alendronate (Fosamax), risedronate (Actonel), zoledronic acid (Reclast), and ibandronate all inhibit osteoclast-mediated resorption. The result is an accumulation of older, more densely mineralized bone. The Fracture Intervention Trial (FIT), which enrolled 6,459 women, showed that alendronate raised lumbar spine BMD by 8.8% over 3 years while reducing vertebral fracture risk by 47%. The T-score improvement is real in the sense that the mineral reading is real. The problem is that bisphosphonates also suppress bone turnover so completely that micro-damage accumulates without remodeling. After 5-10 years of continuous therapy, the BMD keeps rising while atypical femoral fracture risk climbs. The FDA issued a drug safety communication in 2010 noting the association between long-term bisphosphonate use and atypical subtrochanteric femoral fractures.

Practically: a patient on alendronate for 8 years with a lumbar T-score of -1.2 may have higher fracture risk than a bisphosphonate-naive patient with the same score.

Denosumab: Impressive Numbers, Fragile Reversal

Denosumab (Prolia) is a RANK-L inhibitor given as a 60 mg subcutaneous injection every 6 months. The FREEDOM trial (N=7,868) showed denosumab raised lumbar spine BMD by 9.2% and femoral neck BMD by 6.0% over 3 years vs. Placebo, with a 68% relative reduction in vertebral fractures. The T-score gains appear striking on follow-up DEXA. The distortion risk comes at discontinuation: stopping denosumab without transitioning to a bisphosphonate causes rapid rebound bone loss of 6-7% within 12 months and a documented spike in multiple vertebral fractures. A 2019 analysis in the Journal of Bone and Mineral Research documented this rebound vertebral fracture phenomenon. A rising T-score on denosumab should never be interpreted as a signal to stop the drug.

Teriparatide and Abaloparatide: Anabolic Gains Are Real

Teriparatide (Forteo) and abaloparatide (Tymlos) are anabolic agents that stimulate new bone formation rather than just suppressing resorption. The key teriparatide trial (N=1,637 postmenopausal women) showed 9.7% lumbar spine BMD gain at 19 months and a 65% reduction in new vertebral fractures. For these agents, the DEXA improvement reflects a genuine architectural gain. These drugs are limited to 2 years of use by the FDA. After stopping, BMD declines unless a bisphosphonate or denosumab is started promptly.

Strontium Ranelate: The Classic Overestimation Drug

Strontium ranelate (not FDA-approved but used in Europe and sometimes obtained by patients) is the most dramatic DEXA distorter. Strontium has a higher atomic number than calcium, so it absorbs DEXA X-rays more efficiently. Studies in Osteoporosis International showed that strontium ranelate produces apparent BMD increases of 14-20% that overestimate true mineral gain by a factor of roughly 2 to 3. Any patient reporting strontium use requires either a strontium-corrected BMD calculation or a switch to quantitative CT for accurate assessment.

Drugs That Artificially Lower DEXA Scores

These agents reduce the measured T-score, sometimes masking adequate underlying bone density or correctly flagging drug-induced bone loss that needs treatment.

Glucocorticoids: The Most Clinically Significant Suppressor

Prednisone, dexamethasone, hydrocortisone, and inhaled corticosteroids at high doses all accelerate bone resorption while suppressing bone formation. The American College of Rheumatology 2022 guideline on glucocorticoid-induced osteoporosis states that any adult expected to take ≥2.5 mg/day prednisone equivalent for ≥3 months should receive fracture-risk assessment and likely pharmacological therapy. Bone loss is fastest in the first 3-6 months of glucocorticoid exposure: lumbar spine BMD can drop 6-12% in the first year at doses of 7.5 mg/day or higher. The DEXA T-score decline reflects real bone loss here, not artifact. The distortion is that the WHO T-score thresholds were calibrated for primary osteoporosis; glucocorticoid-induced bone has worse quality at any given T-score, so fracture risk is higher than the number suggests.

Aromatase Inhibitors: Estrogen Withdrawal Effect

Anastrozole, letrozole, and exemestane are used in hormone-receptor-positive breast cancer and, increasingly, in off-label settings for estrogen management in men on TRT. These drugs suppress estrogen to near-zero levels. The ATAC trial showed that anastrozole caused significant BMD loss at the lumbar spine (-6.1%) and total hip (-7.2%) over 5 years compared with tamoxifen. A postmenopausal woman starting an aromatase inhibitor should have a baseline DEXA before therapy and a follow-up scan at 1-2 years. The T-score decline is real bone loss driven by estrogen deficiency.

GnRH Agonists and Antagonists

Leuprolide (Lupron), goserelin (Zoladex), and degarelix (Firmagon) suppress gonadal hormone production. Men with prostate cancer on androgen deprivation therapy lose 2-3% of lumbar spine BMD per year. A meta-analysis in the Journal of Clinical Oncology (pooling data from 55 studies) confirmed that androgen deprivation therapy increases osteoporotic fracture risk by approximately 21-45%. Women undergoing GnRH agonist therapy for endometriosis or uterine fibroids experience similar losses. Six months of leuprolide can reduce lumbar spine BMD by 3-4%; add-back estrogen therapy substantially reduces this loss.

Thyroid Hormone Overreplacement

Levothyroxine suppresses TSH below the normal range in thyroid cancer management or through inadvertent overdosing. Supraphysiologic free T4 accelerates bone resorption. A meta-analysis in Annals of Internal Medicine showed that TSH suppression in postmenopausal women was associated with a significant reduction in lumbar spine and hip BMD. Premenopausal women and men appear relatively protected by sex hormones. Checking a DEXA at baseline and rechecking after TSH normalization helps separate drug-induced artifact from primary bone disease.

Heparin: The Forgotten Bone Toxin

Long-term unfractionated heparin, used in pregnancy or for chronic thrombosis, inhibits osteoblast differentiation and activates osteoclasts. Doses above 15,000 units/day for more than 3 months can reduce BMD by up to 30% at the lumbar spine. Low-molecular-weight heparins (enoxaparin, dalteparin) carry a substantially lower but non-zero risk. This was documented in a systematic review in Thrombosis Research. A falling T-score in a pregnant patient on chronic anticoagulation should prompt this consideration.

Drugs With Mixed or Context-Dependent Effects on DEXA

Testosterone Replacement Therapy

TRT raises BMD in hypogonadal men through both direct androgen receptor signaling on bone and through aromatization to estradiol, which is the dominant sex-hormone signal for bone in men. A randomized controlled trial in the New England Journal of Medicine (the Testosterone Trials bone sub-study, N=211) showed that testosterone gel for 12 months increased lumbar spine volumetric BMD by 7.5% and estimated bone strength by 3.6%. The DEXA T-score improvement in a hypogonadal man on TRT reflects a real gain. However, TRT in a eugonadal man at supraphysiologic doses does not produce proportional benefit and may suppress endogenous LH, indirectly reducing testicular testosterone production during any treatment gaps.

Estrogen and Progestogen HRT

Postmenopausal estrogen therapy clearly preserves BMD and reduces fracture risk. The Women's Health Initiative (WHI), which enrolled 16,608 postmenopausal women aged 50-79, showed that combined estrogen-progestogen therapy reduced hip fracture incidence by 34% and vertebral fracture by 35% over a mean of 5.6 years of follow-up. A DEXA improvement of 1-4% per year during HRT is expected and reflects real bone preservation. The distortion risk is subtler: stopping HRT without transitioning to bone-specific therapy causes accelerated bone loss that can erase years of preserved density within 2-3 years.

Antiretroviral Therapy

Tenofovir disoproxil fumarate (TDF), used in HIV treatment and PrEP, causes proximal tubular toxicity that leads to phosphate wasting and secondary bone loss. A meta-analysis of 11 randomized trials showed that TDF-containing regimens were associated with 1-2% greater BMD decline at the lumbar spine compared with tenofovir alafenamide (TAF) or non-tenofovir regimens. For PrEP patients, the FDA label for TDF/emtricitabine recommends considering DEXA in individuals with osteoporosis risk factors. Switching to TAF largely eliminates this effect.

SSRIs and SNRIs

Serotonin receptors on osteoblasts and osteoclasts are well-documented. A cross-sectional analysis of NHANES data (N=5,587) found that SSRI use was associated with a 0.23 SD lower femoral neck T-score after adjusting for age, sex, and BMI. The mechanism involves serotonin transporter (SERT) expression on bone cells. The effect size is modest compared with glucocorticoids or aromatase inhibitors, but it matters in patients with multiple overlapping risk factors.

How to Interpret a DEXA Result When a Patient Takes These Drugs

The following framework guides clinical interpretation when a distorting drug is present:

Step 1. Identify the drug category. Separate drugs into BMD-inflators (bisphosphonates, denosumab, strontium) and BMD-deflators (glucocorticoids, aromatase inhibitors, GnRH agonists, heparin). Mixed agents (TRT, HRT, antiretrovirals) require directional context.

Step 2. Assess duration and dose. A patient on prednisone 5 mg/day for 2 weeks has a negligible DEXA effect. The same patient after 18 months may have lost 8% of lumbar spine BMD. Dose and duration determine whether the T-score shift is clinically meaningful.

Step 3. Apply the FRAX adjustment. The FRAX tool, maintained by the WHO Collaborating Centre at Sheffield, incorporates glucocorticoid use as a separate risk modifier. For patients on ≥7.5 mg prednisone/day, FRAX underestimates fracture risk and the AACE recommends applying a 1.15 to 1.2 multiplier to the hip and major osteoporotic fracture probability before using it to guide treatment thresholds.

Step 4. Consider the scan technique. Lateral vertebral assessment (LVA) and trabecular bone score (TBS) are available on most modern DEXA systems. TBS measures texture irregularity of the spine image and provides information about bone microarchitecture that the raw T-score misses. TBS was validated in the Manitoba cohort (N=29,407 women) as an independent predictor of fracture risk beyond BMD alone.

Step 5. Set the rescan interval appropriately. The DEXA least significant change (LSC) at the lumbar spine is approximately 2-4% (2 SD of the measurement error). Changes smaller than the LSC are noise. Rescanning at 1 year in a patient on high-dose glucocorticoids is appropriate; rescanning at 1 year in a stable bisphosphonate user is not. The ISCD recommends a minimum rescan interval of 1 year for patients at high risk and 2 years for monitoring stable therapy.

When to Raise Bone Density: Drug-Based Treatment Thresholds

The decision to treat is not based solely on T-score. The AACE/ACE 2020 clinical practice guidelines for the diagnosis and treatment of postmenopausal osteoporosis define three risk tiers:

• High risk: T-score at or below -2.5, or prior fragility fracture, or FRAX 10-year hip fracture probability ≥3%, or FRAX major osteoporotic fracture probability ≥20%
• Very high risk: T-score at or below -3.0, multiple fractures, or recent fracture within 2 years, or glucocorticoid use, or very high FRAX
• Imminent fracture risk: Recent fracture within 12 months; anabolic therapy preferred

For high-risk patients, oral bisphosphonates (alendronate 70 mg weekly or risedronate 35 mg weekly) remain first-line due to 10-plus years of safety data and low cost. For very high-risk patients, the Endocrine Society 2019 guideline on pharmacological management of osteoporosis suggests starting with an anabolic agent (teriparatide or abaloparatide) followed by antiresorptive therapy, a sequence called "anabolic first."

Romosozumab (Evenity), a sclerostin inhibitor, raises lumbar spine BMD by 13.3% over 12 months. The ARCH trial (N=4,093) showed romosozumab followed by alendronate reduced new vertebral fractures by 48% vs. Alendronate alone. Romosozumab carries an FDA boxed warning for cardiovascular events; it should not be used in patients with prior myocardial infarction or stroke.

When a High DEXA Score Should Raise Suspicion

A lumbar T-score above +2.0 in an older adult is unusual and warrants investigation before attributing it to good genetics or successful treatment.

Conditions That Falsely Raise Lumbar BMD

Degenerative joint disease, vertebral compression fractures with collapse, overlying aortic calcification, spinal fusion hardware, and Paget's disease of bone all add mineral mass to the scan region without improving skeletal strength. A review in the Journal of Clinical Densitometry noted that lumbar spine BMD readings can be elevated by 10-30% in the presence of severe osteoarthritis at L1-L4. When lumbar spine and hip results diverge by more than 1.0 T-score unit, artifact is the probable explanation. In these cases, the hip T-score is the more reliable clinical guide.

Strontium Supplementation as a Hidden Confounder

Strontium carbonate supplements are sold without prescription. Patients may not mention them because they do not consider supplements to be "medications." Any patient with an unexpectedly high or rapidly rising DEXA score should be asked specifically about strontium supplementation. Strontium's heavier atomic weight means it absorbs X-rays more efficiently than calcium on a molar basis, producing phantom BMD elevations. Stopping strontium for 3-6 months before a scan eliminates most of the artifact.

Practical Guidance for Clinicians and Patients

Order a baseline DEXA before starting any of the following: glucocorticoids expected to last more than 3 months, aromatase inhibitors, GnRH agonists, long-term heparin, or antiretroviral therapy with TDF. Document the specific machine and facility, because switching DEXA machines mid-treatment introduces cross-calibration error that can mimic real change.

For patients already on bisphosphonates for 5 or more years, the AACE and the American Society for Bone and Mineral Research recommend a structured "drug holiday" assessment. A 2019 NEJM review of long-term bisphosphonate use concluded that a 5-year holiday is appropriate for patients with femoral neck T-scores above -2.5 who are not at high fracture risk after the initial 5-year course. During the holiday, DEXA should be repeated every 2 years because residual drug in bone continues to provide partial protection.

The USPSTF 2018 final recommendation advises screening all women age 65 and older and younger postmenopausal women whose 10-year fracture probability, calculated by FRAX without BMD, equals or exceeds that of a 65-year-old white woman (approximately 9.3% for major osteoporotic fracture). Men are not covered by the USPSTF recommendation; screening decisions in men rely on the AACE and Endocrine Society guidelines, which suggest screening men over 70 or men over 50 with risk factors such as hypogonadism, glucocorticoid use, or prior fragility fracture.

As the 2019 Endocrine Society clinical practice guideline states: "Pharmacological treatment should be started in patients with osteoporosis at high risk of fracture to reduce fracture incidence and associated morbidity and mortality." That recommendation applies regardless of which drug caused the T-score to reach the treatment threshold.