Whether you can keep your bra on during a bone density test depends entirely on the bra. An underwire bra needs to come off because the metal sits directly in the scanning zone and can distort your results. A soft sports bra or bralette with no metal hardware is usually fine to wear, though some clinics will ask you to change into a gown regardless. The distinction matters because even small artifacts can shift the bone mineral density reading enough to affect your diagnosis or treatment decisions.
Why Underwire Bras Specifically Cause Problems
A bone density test, formally called a DXA scan, works by passing two low-energy X-ray beams through your body and measuring how much each beam is absorbed. Bone absorbs more energy than soft tissue, and the scanner uses that difference to calculate bone mineral density (BMD). Any dense object in the scan path, especially metal, absorbs the beams in ways the software misinterprets as bone. The result is a falsely elevated BMD reading at that location.
Clinical guidelines are explicit about this. A technical review in the Journal of Nuclear Medicine Technology states that “the patient must remove all objects from their pockets or body in the scan field, such as wallets, cell phones, underwire bras, watches, and bracelets.”1Journal of Nuclear Medicine Technology. Improving DXA Quality by Avoiding Common Technical and Diagnostic Pitfalls: Part 1 Underwire bras make the list alongside phones and jewelry because the wire curves directly over the ribcage and lower thoracic spine, landing squarely in the scan field for a standard lumbar spine DXA.
A study using phantom torsos (calibration models that simulate human bodies) tested exactly how much bra wires shift the numbers. In a low-BMD torso model, bra wires measurably altered the L1 through L4 bone density reading.2Journal of Clinical Densitometry. The Effect of Common Artifacts Lateral to the Spine on Bone Mineral Density in the Lumbar Spine That finding is especially concerning because people being screened for osteoporosis already have lower bone density, meaning they are the exact population where the artifact has the greatest chance of masking a real problem or producing a misleading improvement between visits.
What the Scanner Actually Looks At
Understanding where the X-ray beam travels helps explain why some clothing items are an issue and others are not. A standard DXA exam scans two regions. For the spine, the scan captures a posteroanterior image of the first through fourth lumbar vertebrae (roughly the area from your lower ribs to your hip bones). For the hip, it captures the top of the femur, including the femoral head and the greater trochanter.1Journal of Nuclear Medicine Technology. Improving DXA Quality by Avoiding Common Technical and Diagnostic Pitfalls: Part 1
The spine scan field stretches from a portion of the lowest thoracic vertebra down through the iliac crests. The underwire in a bra sits right around the lower thoracic and upper lumbar area, so it overlaps with the top of the lumbar spine image. A front-closure bra with a metal clasp can also land in this zone. For the hip scan, a bra is far enough away that it usually is not a concern. But since most standard bone density exams include both regions in the same appointment, the technologist typically asks you to remove the bra before you even lie down rather than taking it off between scans.
Sports Bras, Bralettes, and the Fabric Question
If your bra has no underwire, no metal hooks, no metal clasps, and no metallic decorative elements, it is unlikely to interfere with the scan. A basic cotton sports bra or a pull-on bralette is generally considered safe. However, the story gets a little more complicated when you consider fabric composition.
Research on how textiles affect DXA results found that not all fabrics are equal. Dense textiles like wool and denim, as well as fabrics containing reflective material or metallic thread, measurably changed fat mass and lean mass readings. The study recommended avoiding clothing made of those materials during a DXA scan.3PubMed Central. Do Textiles Impact DXA Bone Density or Body Composition Results? While a thin cotton or nylon sports bra is unlikely to hit this threshold, some athletic bras incorporate metallic thread for odor control (silver-infused fabrics are common in performance wear) or have reflective safety strips. If your sports bra has any kind of shimmer, reflective panel, or antimicrobial silver threading, play it safe and leave it in the changing room.
The safest option if you want to keep something on is a plain, lightweight cotton or standard polyester sports bra with no hardware whatsoever. Many clinics will offer you a gown anyway, and changing takes about 30 seconds, so if you are unsure about your bra’s construction, just swap into the gown.
What Else to Remove Before the Scan
Bras get most of the attention in pre-scan instructions because they are the item people most commonly forget about, but the same principle applies to anything dense or metallic in the scan zone. Belts with metal buckles, jeans with rivets, and pants with zipper flies can all fall within the hip scan field. Necklaces or body piercings in the torso area can create small but measurable artifacts. Even items in your pockets, like keys, coins, or a phone, need to be removed.
One artifact source that surprises people is calcium supplements. A study found that taking calcium tablets within 30 minutes of a spine DXA could affect the measured BMD, with about a third of subjects showing changes that exceeded the scan’s precision threshold. Tablets were visible in the scan in roughly half of cases. The researchers concluded that patients should avoid calcium tablet ingestion before a spine exam.4PubMed Central. Calcium supplement ingestion may alter lumbar spine bone mineral density measurement If you take a daily calcium supplement, try to take it after your appointment rather than before. This is a detail most appointment reminder letters do not mention.
When Internal Metal Cannot Be Removed
External objects like bras and jewelry are easy to deal with because you take them off. Internal hardware is a different challenge. Spinal implants, surgical screws, and joint replacements all create artifacts that the technologist cannot remove.
A study using a phantom body with an extraneous spinal implant found that total body bone mineral density jumped from 1.216 to 1.305 g/cm² with the implant in place, an increase that was both statistically significant and well beyond the scan’s precision limits. Trunk-level bone mineral content increased by over 30%.5PLoS ONE. Does a spinal implant alter dual energy X-ray absorptiometry body composition measurements? In other words, the implant fooled the scanner into dramatically overestimating bone density, which in a real patient could mask osteoporosis entirely.
Even small metal objects inside the body can matter. Research on tantalum surgical clips (used in some operations to mark tissue) showed that while the clips did not significantly change the overall L1-L4 reading in a high-density spine, they did have the potential to alter individual vertebral body measurements and the composite L1-L4 reading in a low-density spine.6PubMed. Black hole artifacts-a new potential pitfall for DXA accuracy? If you have had any spinal surgery or abdominal surgery that involved metal clips, mention it to the technologist. They may exclude the affected vertebra from the analysis or rely on the hip site instead.
Common Positioning Mistakes That Affect Results More Than Clothing
Clothing artifacts are worth worrying about, but they are not the biggest source of error in DXA scanning. How you are positioned on the table matters at least as much. A study examining technologist performance found that before retraining, about a third of lumbar spine scans failed to include both iliac crests in the image, roughly 30% were not straight, and about 20% were not centered. For hip scans, over half had straightness errors and about a fifth lacked proper internal rotation of the leg.7PubMed. Errors in Patient Positioning for Bone Mineral Density Assessment by Dual X-Ray Absorptiometry: Effect of Technologist Retraining
After technologist retraining, those error rates dropped dramatically, in many cases falling below 5%. The takeaway for you as a patient is that the skill of the technologist running your scan has a real effect on accuracy. If something feels awkward about your positioning, or if the technologist seems to rush through setup, it is worth asking whether everything looks right. You should also try to go to the same facility each time you have a bone density test, because small differences in machine calibration and positioning habits between clinics can make it look like your bone density changed when it actually did not.
Peripheral Scans and Forearm Measurements
Not all bone density tests scan the spine and hip. Some screening tests use a smaller device that measures the forearm, usually at the wrist. These peripheral DXA scans are less common for full diagnosis but are sometimes used at health fairs or in offices that do not have a full-body scanner. Clothing interference is still relevant here. A study found that clothing covering the forearm, along with certain positioner artifacts, could affect the one-third radius bone density measurement.8PubMed Central. Positioner and clothing artifact can affect one-third radius bone mineral density measurement
For a forearm scan, push your sleeve well above the scanning area or remove the garment covering that arm. A rolled-up sweater bunched at the elbow can sometimes drift down into the scan field, so taking the arm out of the sleeve entirely is the most reliable approach.
How Much Radiation a DXA Scan Involves
Some people worry about removing clothing for a DXA because they assume the test involves significant radiation, similar to a CT scan. In reality, DXA scans deliver an extremely small dose. A review of radiation exposure from osteoporosis imaging techniques reported that the effective dose from a standard DXA scan is far lower than that of a chest X-ray or a CT scan.9PubMed Central. Radiation exposure in X-ray-based imaging techniques used in osteoporosis Another analysis placed spinal DXA morphometry below 60 microsieverts, which is comparable to a day or two of natural background radiation from the environment.10PubMed. Radiation exposure in bone mineral density assessment
The low radiation dose means the scan is safe to repeat at regular intervals, typically every one to two years for people being monitored for osteoporosis. It also means there is no clinical reason to keep extra layers of fabric between you and the scanner for “protection.” The clothing concern is about scan accuracy, not radiation shielding. A cotton T-shirt or hospital gown does nothing to block the beam, and that is fine because the beam is so weak it poses no meaningful health risk.
What to Wear to Your Appointment
Knowing all of this, the simplest strategy is to dress for the scan rather than figuring out what to remove once you arrive. Wear loose, lightweight clothing with no metal anywhere: elastic-waist pants, a T-shirt, and a sports bra without clasps or wires. Skip the jeans, skip the belt, and leave the jewelry at home. If you take calcium supplements, hold your dose until after the appointment. Bring a list of any surgeries you have had that involved metal implants so the technologist knows what to expect in the images.
Most facilities will have a gown available if you arrive in something unsuitable, but dressing simply means less time in the changing room and less chance that you forget to remove a piece of jewelry or a pocket item. The scan itself usually takes ten to fifteen minutes once you are positioned, and the entire appointment is often under half an hour. A little forethought about what you are wearing can make the whole experience faster and, more importantly, ensure the numbers your doctor receives are accurate.