A DEXA scan is one of the safest, fastest and most precise ways to measure body fat, lean muscle, visceral fat and bone density. A whole-body scan uses less radiation than a single day of natural background exposure. This FAQ answers the questions we hear most at DEXASCAN.COM: safety, how the technology works, how to read results from Hologic and GE Lunar scanners, and how to track everything in the free DEXASCAN app.
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Safety & Health
Is a DEXA scan safe?
Yes. DEXA uses a very low dose of X-ray. Researchers consider the dose negligible, and it is far lower than CT scans and many other imaging tests (PMC). There are no needles, dyes, injections or downtime.
How much radiation is in a whole-body DEXA scan?
A whole-body scan on current scanners delivers about 4–5 microsieverts (µSv). That is less than the roughly 6.7 µSv we each absorb every day from natural background radiation (PMC). Reviews generally place a single whole-body scan under 10 µSv, about one day at sea level (Shepherd et al., NIH). For comparison, a head CT is about 2,000 µSv.
Does the dose differ between Hologic and GE scanners?
Slightly, depending on the model and scan mode. Both are very low. Published figures for adult whole-body scans run from well under 1 µSv on some GE Lunar models to about 4–8 µSv on Hologic models (Advances in Rheumatology). Every one of these is a tiny fraction of everyday exposure.
Who should not get a DEXA scan?
- Pregnant or possibly pregnant: skip the scan as a precaution and tell the technician.
- Recent contrast or nuclear medicine test (barium study, CT with contrast, bone scan): wait until it clears, usually 7–10 days. Ask the provider for their window.
- Above the table's weight or width limit: see the Technology section. Larger bodies can often be scanned with offset scanning.
Can I get scanned with metal implants, joint replacements or a pacemaker?
Usually yes. DEXA is not an MRI, so metal is not a safety issue. Metal can affect readings in that area, so tell the technician. They can exclude the area or note it on your report.
How often is it safe to scan?
Most people rescan every 8–12 weeks while working toward a goal. That is often enough to see real change in fat and muscle, with a minimal total dose. For bone density alone, your doctor may recommend every 1–2 years.
Is DEXA a medical diagnosis?
A body composition DEXA is a wellness and tracking tool. Bone density readings from a body composition scan are not a substitute for a dedicated hip and spine bone density exam ordered by your doctor. Share your results with your healthcare provider for medical decisions. Learn more about bone density.
Who benefits most?
Anyone managing weight, on a GLP-1 medication, going through menopause, training for performance, or focused on longevity. Men can benefit too. See Should Men Get a Bone Density Test? and our GLP-1, Weight Loss & Peptides guide.
How DEXA Technology Works
What does DEXA stand for?
Dual-Energy X-ray Absorptiometry. The scanner passes two low-energy X-ray beams over your body. Bone, lean tissue and fat absorb each energy differently. Software uses that difference to measure all three, pixel by pixel, across your whole body (Shepherd et al., NIH).
Why is DEXA called the gold standard?
It directly measures three compartments (fat, lean and bone) instead of estimating from weight, height or electrical signals. It also breaks results down by arm, leg, trunk, android (belly) and gynoid (hip) regions. See the evidence.
How does it compare with other methods?
| Method | What it measures | Regional detail | Typical use |
|---|---|---|---|
| DEXA | Fat, lean and bone, directly | Arms, legs, trunk, visceral fat | Clinical-grade baseline and progress tracking |
| Smart scale (BIA) | Estimates from electrical resistance | Limited; varies with hydration | Daily trends between scans |
| Skinfold calipers | Skin thickness at a few sites | None | Quick field estimate |
| BMI | Weight vs. height only | None | Population screening |
The best approach uses both: DEXA for accuracy and a home scale like the DEXA+ Body Fat Scale for daily trends.
Who makes the scanners?
The two leading manufacturers are Hologic (Horizon and Discovery models) and GE HealthCare Lunar (iDXA and Prodigy models) (PMC). Both are excellent, widely used in research and clinics, and both are in the DEXASCAN.COM provider network.
What is the difference between Hologic and GE technology?
The core principle is the same. The differences are in hardware and software:
- Beam shape: GE uses a narrow-angle fan beam. Hologic uses a wide-angle fan beam (PMC).
- Software: Hologic uses APEX software. GE uses enCORE software.
- Calibration: each brand uses its own proprietary calibration and algorithms. That is why results are not interchangeable (see the Results section).
How precise is DEXA?
Very. On both a GE Lunar iDXA and a Hologic Horizon A, repeat-scan precision for body fat % is under 1% (UNM, Hologic). That precision is what lets you see real change from scan to scan.
How long does a scan take?
Plan on 20–30 minutes for the full appointment. The scan itself takes a few minutes up to about 15, depending on the machine and your size. You lie still on your back, fully clothed.
Is there a size or weight limit?
Yes, and it depends on the model. Table limits range from roughly 350 lb on some older models to 450 lb on the GE Lunar iDXA (UNM, NCCOR). If you are wider than the scan area, technicians can use offset scanning (called reflection mode on Hologic and mirror mode on GE). Studies show it agrees well with standard scans (Shepherd et al., NIH). Call your provider to confirm before booking.
How should I prepare?
- Scan in the morning if you can, ideally fasted or after a light meal.
- Hydrate normally. Avoid big changes in fluid or salt the day before.
- Skip hard workouts for 12–24 hours before.
- Skip calcium supplements for 24 hours.
- Wear light clothing with no metal: no zippers, underwire, jewelry or snaps.
- For progress scans, repeat the same routine, time of day and provider every time.
Understanding Your Results: Hologic vs. GE
What will my report show?
Every whole-body DEXA report shows body fat %, fat mass, lean mass and bone mineral content, broken down by arms, legs and trunk. It also shows android (belly) and gynoid (hip) fat and a visceral fat estimate. Both brands compare you with U.S. population data from the national NHANES survey (Shepherd et al., NIH).
How do Hologic and GE reports differ?
They measure the same things but label and present them differently.
| Report item | Hologic (Horizon, Discovery) | GE Lunar (iDXA, Prodigy) |
|---|---|---|
| Software | APEX | enCORE |
| Visceral fat | InnerCore VAT: mass, volume and area (cm²) | CoreScan VAT: mass and volume |
| How VAT is estimated | Total abdominal fat minus the subcutaneous layer, across the abdomen | Subcutaneous fat subtracted from total fat in the android (belly) region |
| Fat indices | Fat Mass Index (FMI), android/gynoid ratio, trunk/leg and trunk/limb fat ratios | Android/gynoid ratio, trunk/limb and trunk/leg ratios; FMI on many reports |
| Muscle indices | Lean/height² and appendicular lean/height² (ALMI) | Lean mass by region; appendicular lean mass index on many reports |
| Percentiles | Young Normal (YN) and Age Matched (AM), from NHANES scans done on Hologic systems | NHANES-based references converted to GE, plus GE-specific reference data |
| Visual | Fat/lean/bone color image | Color-coded body map of fat, lean and bone |
Sources: Hologic sample report, Hologic body composition brochure, PMC on Hologic VAT, GE CoreScan, PMC, GE reference values, PMC, NCCOR.
Can I compare a Hologic scan with a GE scan?
Not directly. Each brand uses its own calibration and algorithms, so the same person gets slightly different numbers on each. One comparison found average differences of about 1.4 percentage points in body fat % between the brands (PMC). Lean mass and appendicular lean mass also differ significantly, even though the two correlate strongly (PMC).
Researchers have published conversion equations that close these gaps (JBMR Plus, 2024). For visceral fat, GE and Hologic results correlate very closely and classify metabolic risk in a largely similar way (Obesity, 2023).
Bottom line: for true progress tracking, scan on the same brand, ideally the same machine and provider, every time. If you have to switch, treat the new scan as a fresh baseline.
Can I compare a GE iDXA with a GE Prodigy?
They are close but not identical. Visceral fat on the Prodigy correlates very closely with the iDXA, but the iDXA is more precise from scan to scan (JCD). Sticking with one machine is still best.
What do the percentiles mean?
- Young Normal (YN): how you compare with healthy young adults of your sex.
- Age Matched (AM): how you compare with people your age and sex.
For body fat and visceral fat, a lower percentile is generally better. For lean mass and ALMI, a higher percentile is generally better.
What is a good visceral fat number?
Lower is better. Visceral fat is linked to insulin resistance, heart disease, fatty liver and high blood pressure (PMC). Because Hologic and GE estimate it differently, compare your number with your own past scans on the same brand rather than with a friend's report or a chart from another brand. Your provider can explain where you fall.
What are FMI and ALMI?
- Fat Mass Index (FMI): fat mass divided by height squared (kg/m²). Unlike BMI, it is not thrown off by muscle (PMC).
- Appendicular Lean Mass Index (ALMI): muscle in your arms and legs divided by height squared. It is a key marker for healthy aging and for protecting muscle during weight loss (PLoS ONE).
Does the bone density on my body composition report diagnose osteoporosis?
No. The whole-body bone reading is useful for trends. Osteoporosis is diagnosed from a dedicated hip and spine bone density exam. If your number looks low, talk with your doctor.
Why did my results change more than expected?
Hydration, a big meal, a hard workout, clothing and positioning can all shift results slightly. Following the same prep routine every time keeps your comparisons clean. See the prep checklist in the Technology section.
Using the DEXASCAN App
What is the DEXASCAN app?
It is a free app that keeps all your results in one place and shows how they change over time. It tracks DEXA, VO₂ Max, RMR and blood markers (App Store). Learn more on DEXASCAN.COM.
Where do I download it?
Download DexaScan on the App Store. It is free and works on iPhone and iPad (iOS 14 or later), Apple-silicon Macs and Apple Vision Pro.
Does it work with Hologic and GE results?
Yes. The app tracks your numbers, not a specific machine, so you can log results from any provider. For clean trend lines, keep using the same brand and provider for each scan, as explained in the Results section.
How do I add my scan results?
- Open the app and go to your dashboard.
- Tap Add a Scan.
- Enter the values from your DEXA report, such as body fat %, lean mass, fat mass, visceral fat and bone density.
- Add VO₂ Max, RMR or blood marker results whenever you have them. Resting heart rate is optional.
- Save. Your new scan appears in your scan table and on your graphs.
Need a scan first? Tap Buy a Scan in the app or book on DEXASCAN.COM.
What can I see in the app?
- Dashboard: interactive graphs of your progress.
- Scan table: every past scan in one list.
- Lean vs. fat tissue graphs: see whether you are gaining muscle or losing fat.
- RMR graph: how your metabolism changes over time.
- Body mass, fat % and bone density: side by side for each scan.
- PDF reports: generate a PDF to share with your coach or doctor.
- Units: choose the measurement units you prefer.
Source: App Store listing and release notes.
Does the app connect to the DEXA+ Body Fat Scale?
Yes. The DEXA+ Body Fat Scale syncs to the free DEXASCAN app alongside your DEXA history and also connects to Apple Health. Use the scale for daily trends and DEXA every 8–12 weeks for clinical accuracy.
Is my data private?
The App Store privacy label for DexaScan states that the developer does not collect data from the app (App Store). See our Privacy Policy and HIPAA Policy for details.
How should I use the app between scans?
- Log every DEXA, VO₂ Max and RMR result the day you get it.
- Weigh in on the DEXA+ scale at the same time each morning.
- Review your lean vs. fat graph before each rescan to see if your plan is working.
- Pair it with the free 30-day Kick-Start and 90-day tracking guides included with any purchase.
Booking Your Scan
How do I book?
Search by ZIP code or city, pick a validated provider, and buy online. You will get booking instructions within minutes. DEXASCAN.COM has 400+ verified providers nationwide and has matched clients with trusted providers since 2021.
How much does it cost?
Scans start at $89 with upfront prices and no surprise fees. HSA and FSA cards are accepted. Use code HOLIDAY for $10 off any assessment for a limited time.
Should I add RMR or VO₂ Max testing?
If your goal is fat loss or performance, yes. RMR testing measures the calories you burn at rest. VO₂ Max testing measures cardiovascular fitness and your best training zones. Both log right into the DEXASCAN app.
Still have questions?
Read our full FAQ page, browse the Learn center, or call a real person at 786-668-DEXA.
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