Lightweight, metal-free clothing with no zippers, snaps, or underwire gives you the cleanest DEXA scan results. A plain cotton T-shirt and elastic-waist sweatpants or athletic shorts are the standard recommendation, and research confirms that certain everyday fabrics can measurably throw off your readings. But clothing is only one piece of preparation. What you eat, drink, and do in the hours before your appointment also matters, and some of those details rarely make it onto the scheduling reminder your clinic sends.
Why Your Clothing Affects the Results
A DEXA scanner passes two low-energy X-ray beams through your body and uses the difference in how those beams are absorbed to distinguish bone from soft tissue and fat from lean mass. Anything between you and the detector that absorbs or reflects those beams gets read as part of your body. The scanner cannot tell the difference between a dense wool sweater and a layer of tissue, so it folds the clothing into your measurements.
A study testing a range of common fabrics directly on a DEXA scanner found that dense textiles like wool, denim (both cotton and blended), and materials containing metallic thread or reflective coatings significantly altered bone mineral density and body composition results. Even small amounts of reflective material shifted mass measurements by roughly a quarter of the least significant change, the threshold used to decide whether a real change has occurred between two scans. Fat and lean mass readings were both affected by metallic thread, wool, blend denim, and shiny polyester. The researchers concluded that clothing made of dense textiles or anything with reflective material and metallic thread should be avoided during scanning.1PubMed. Do Textiles Impact DXA Bone Density or Body Composition Results?
Plain cotton, thin polyester blends, and basic jersey knits performed fine in the same testing. The safest choice is a single layer of lightweight, non-metallic fabric. If you have athletic wear without any logos made of glitter or metallic print, that works well. Many clinics keep a paper or cotton gown available as a backup, so if you arrive in jeans and realize your mistake, you can usually change.
Metals, Jewelry, and Piercings
Metal creates a more dramatic problem than fabric. Zippers, bra underwires, belt buckles, and snap buttons are all dense enough to block or heavily attenuate the X-ray beams. The scanner sees these as extremely dense objects and tries to categorize them, producing what researchers call a “black-hole” artifact. A Monte Carlo simulation study showed that materials like stainless steel, titanium alloy, and gold all attenuate the X-ray photons substantially, and in a torso phantom, piercing objects appeared as holes punched through the vertebral images. Both high-density and low-density artificial materials get eliminated during the scanner’s dual-energy subtraction process, which is what creates the artifact in the first place.2PubMed Central. Artificial High- and Low-density Materials in Bone Mineral Densitometry Using Dual-energy X-ray Absorptiometry: A GATE Monte Carlo Simulation of “Black-hole” Artifact
The practical takeaway is straightforward: remove all jewelry before your scan. Necklaces, rings, watches, earrings, and any body piercings you can take out should come off. If you have a piercing you cannot remove, mention it to the technologist so they can note it and, if possible, position the scan area to avoid it. A belly button ring sitting right over a lumbar vertebra is a different problem than a nose stud during a hip scan.
A Quick Checklist of What to Wear and What to Remove
Since the specifics matter, here is what works and what does not:
- Wear: A plain cotton or thin polyester T-shirt, elastic-waist sweatpants, athletic shorts, or leggings without metallic logos or reflective strips. Socks are fine.
- Remove before scanning: Bras with underwire, jeans or pants with metal buttons and zippers, belts, watches, all jewelry, hair clips or barrettes if scanning the spine, and shoes.
- Avoid entirely: Wool sweaters, denim of any kind, garments with metallic thread or sequins, shiny or glitter-printed athletic wear, and compression garments with embedded metal fibers.
If you are getting a whole-body composition scan rather than just a hip-and-spine bone density check, clothing choices matter even more because the scanner is measuring every region. A sports bra without underwire and plain shorts are ideal for a full-body scan.
Calcium Supplements and the Morning-Of Question
If you take calcium supplements, the timing relative to your scan matters. An undissolved calcium tablet sitting in your gastrointestinal tract can overlap with your lumbar spine on the scan image. One study found that a 500 mg calcium tablet placed over the scan area increased measured bone mineral density of a single vertebral body by as much as 12.6%, with larger effects at higher calcium doses and in people with lower baseline bone density. The overall L1-L4 measurement was less affected, but individual vertebral readings could shift enough to matter.3PubMed. Effect of calcium tablets on interpretation of lumbar spine DXA scans
A separate study tested what happens when people simply swallow their normal calcium supplement before a scan. Within 30 minutes of ingestion, more than a third of subjects showed bone density changes outside the least significant change threshold, and about half had visible tablets on their scan images. The researchers recommended that patients skip calcium tablets before a spine DEXA exam.4Journal of Clinical Densitometry. Calcium Supplement Ingestion May Alter Lumbar Spine Bone Mineral Density Measurement
Most clinics now advise skipping calcium supplements for at least 24 hours before your scan. If you forget and take one the morning of, let your technologist know. They may decide to proceed and note the supplement, or they may reschedule the spine portion of the exam depending on the timing.
Contrast Dye and Recent Medical Imaging
If you have had a CT scan, MRI with contrast, or a nuclear medicine study recently, the timing can affect your DEXA results. A study measuring the impact of CT contrast agents on DEXA found that scans performed immediately after a contrast-enhanced CT showed whole-body bone mineral content inflated to about 125% of baseline, total fat mass dropped to about 75% of baseline, and lean body mass rose to about 110% of baseline. These are large distortions. However, when the DEXA was repeated seven days later, results were back to baseline with no statistically significant difference.5PubMed. Effect of diagnostic radioisotopes and radiographic contrast media on measurements of lumbar spine bone mineral density and body composition by dual-energy x-ray absorptiometry
The safe rule is to wait at least a week after any contrast-enhanced imaging before having a DEXA scan. If you have a nuclear medicine study involving radioactive tracers, the same one-week buffer applies. When scheduling, mention any recent imaging to the front desk so they can space things out properly.
Eating, Drinking, and Hydration
You do not need to fast before a DEXA scan, but what is in your stomach and how much fluid you have on board can nudge the numbers. A study of 100 people who drank 500 mL of water (about two cups) immediately before scanning found a significant increase in measured lean mass of roughly half a kilogram and a decrease in body fat percentage of about 0.16%. Fat mass itself did not change significantly, but the water was read as lean tissue, which shifted the ratio.6Clinical Nutrition. The effects of acute water ingestion on body composition analyses via Dual-Energy X-Ray Absorptiometry
Those numbers are small in absolute terms, but if you are tracking body composition over time and chugging a liter of water before one scan but not the next, you are introducing noise into your trend. The practical advice: drink normally, but do not slam a large bottle of water right before your appointment. If you are using DEXA scans to track progress over months, try to keep your fluid intake roughly consistent in the couple of hours before each scan.
Should You Exercise Before Your Scan?
Working out before a DEXA scan is another variable people rarely think about. Exercise shifts fluid between compartments in your body through sweating, blood flow redistribution, and glycogen depletion, and all of that registers on the scanner. Research on active people found that exercise and its related practices of food and fluid intake changed mean estimates of total and regional body composition by amounts ranging from trivial to small but meaningful, and also increased the typical measurement error by about 10%.7PubMed Central. Effects of exercise sessions on DXA measurements of body composition in active people
A 10% increase in measurement error is not catastrophic for a single diagnostic scan, but it can easily swamp the small real changes you are trying to detect between two scans taken months apart. If your DEXA is scheduled for the afternoon, skip your morning workout or at least keep it light. If you are an athlete or coach using DEXA to monitor training adaptations, schedule scans at a consistent time of day, ideally in the morning before any exercise.
Patches, Tape, and Topical Products
Nicotine patches, hormone patches, lidocaine patches, and even thick layers of topical cream or ointment can create small artifacts on DEXA images. The patches contain adhesives and sometimes metallic foil backing that the scanner picks up. The same principle applies to bandages with metal clasps or surgical tape with embedded wire.
Remove any patches you can safely remove before the scan, and wipe off thick layers of lotion or topical medication from the areas being scanned (typically the torso and hips for a standard bone density test, or the full body for a composition scan). If a patch cannot be removed for medical reasons, let the technologist know its location so they can account for it.
What Happens on the Table
How you are positioned on the scanner table is one of the biggest sources of error, and it is mostly out of your hands. Research evaluating real-world clinical practice found surprisingly high rates of improper positioning. In one audit of 113 hip and spine reports, the spine was not straight in nearly half of the images, close to 40% of spinal images did not include the correct vertebral landmarks, and about 41% of hip scans had the femur angled to one side.8PubMed. Evaluation of the patient positioning during DXA measurements in daily clinical practice
Femoral rotation is a particular problem. Even small differences in how your leg is rotated during a hip scan change the measured bone density of the femoral neck, which is a critical diagnostic site. Studies using positioning jigs to lock the femur in place reduced precision error by almost 50% compared to the standard foot block most scanners come with.9PubMed. Effect of femoral rotation on bone mineral density measurements with dual energy X-ray absorptiometry
You cannot control the technologist’s skill, but you can help by lying still, following their instructions about leg position, and not shifting once you are set up. If the technologist places a foam block or strap between your feet, do not adjust it yourself. That block exists to keep your hip rotated to a standardized angle, and moving it even slightly changes the geometry the scanner sees.
If You Have Metal Implants or Surgical Hardware
Joint replacements, spinal fusion hardware, plates, and screws are permanent metal in the scan field, and they create the same black-hole artifacts that removable jewelry does. The difference is you cannot take them out. For people with a hip replacement on one side, the technologist will scan the opposite hip. If both hips have been replaced, the scan typically shifts to the forearm or another site.
Spinal hardware is trickier because the lumbar spine is one of the two standard diagnostic sites. When rods, screws, or cages are present, the affected vertebrae are usually excluded from the analysis, and the remaining vertebrae are used to calculate the score. If the hardware spans the entire lumbar region, the spine measurement may not be usable at all. Let the clinic know about any implants when you schedule so they can plan which sites to scan and allow enough time.
Preparation When You Are Tracking Changes Over Time
A single DEXA scan for diagnostic purposes is fairly forgiving of small preparation inconsistencies. Where preparation becomes genuinely important is when you are comparing two or more scans over time to track bone loss, treatment response, or body composition changes. The differences you are trying to detect between scans are often quite small, and every uncontrolled variable adds noise that can mask real change or create the illusion of change that is not there.
For longitudinal tracking, try to standardize as many conditions as possible between scans:
- Same facility: Different scanner brands and even different machines of the same brand can give slightly different readings. Stick with the same machine if you can.
- Same time of day: Body water distribution shifts throughout the day. Morning scans before eating or exercising are the most reproducible.
- Same clothing: Wear the same type of outfit each time. If you wore a gown for one scan, wear a gown for the next.
- Same hydration and meal pattern: Do not fast for one scan and arrive after brunch for the next.
- Same supplement schedule: Skip calcium supplements before every scan, not just some of them.
Scanner Limitations for Larger Bodies
Standard DEXA scanner tables have a weight limit, usually around 300 to 450 pounds depending on the manufacturer, and the scan field has a fixed width. If your body extends beyond the edges of the scan area, part of you is not measured, which underestimates total body composition values. Research on this problem found that the most practical workaround for people who do not fit entirely under the scanning arm is to measure specific regions like the thigh or abdomen, or to perform two half-body scans and combine them mathematically. The half-body approach is more time-consuming but can give a reasonable estimate of total body fat, though the researchers noted it needs more validation.10PubMed Central. Measuring body composition in overweight individuals by dual energy x-ray absorptiometry
If you know this could be an issue, call the facility in advance and ask about their scanner’s specifications and whether they have experience with half-body scan protocols. Not every technologist routinely performs them, and the software processing is slightly different.
Radiation Exposure in Context
Some people worry about the radiation from a DEXA scan, and it is worth putting the numbers in perspective. The effective dose from a standard hip or spine DEXA scan is extremely small, on the order of a few microsieverts, which is comparable to the natural background radiation you receive in a single day. For reference, the worldwide average background radiation exposure is about 2.4 millisieverts per year.11PubMed Central. Radiation exposure in X-ray-based imaging techniques used in osteoporosis A DEXA scan delivers a tiny fraction of that annual dose. Research using anthropomorphic phantoms concluded that a patient undergoing DEXA examinations over a lifetime has a negligible increased risk of developing cancer, regardless of which scan mode or body site is used.12Journal of Clinical Densitometry. Dose Absorption in Lumbar and Femoral Dual Energy X-ray Absorptiometry Examinations Using Three Different Scan Modalities: An Anthropomorphic Phantom Study
The one exception is pregnancy. DEXA scans are not performed on pregnant women, not because the dose is dangerous in absolute terms, but because any unnecessary radiation to a developing fetus is avoided as a precaution. If there is any chance you are pregnant, tell the technologist before the scan.
What to Expect During the Scan Itself
The scan is quick and painless. You lie flat on a padded table, and the scanning arm passes slowly over the areas being measured. A spine-and-hip bone density test typically takes five to ten minutes. A full-body composition scan takes closer to ten to twenty minutes. You need to stay still during the scan, but you do not need to hold your breath or do anything active. There is no enclosed tube, so claustrophobia is not a concern.
The technologist will position you for each site, often placing a foam block between or under your legs for hip scans, and may use a strap to help keep your feet at the correct angle. They may ask you to straighten up or shift slightly on the table. Once you are positioned, the machine does the rest. You will not feel the X-ray beam. Some people are surprised by how uneventful the whole experience is, especially if they are used to more involved imaging procedures.