How to Prepare for a Bone Density Scan

Preparing for a bone density scan is straightforward and requires very little disruption to your day. The main steps are to stop taking calcium supplements for at least 24 hours beforehand, wear clothing without metal zippers or buttons, and let the technologist know about any recent medical procedures that involved contrast dye or radioactive tracers. The scan itself is painless, takes about 10 to 20 minutes, and involves far less radiation than a standard X-ray. But a few details in your preparation can genuinely affect the accuracy of your results, so they are worth getting right.

Skip Calcium Supplements Before Your Appointment

The single most important preparation step is to stop taking calcium supplements before the scan. Undissolved calcium tablets sitting in your gastrointestinal tract can overlap with your spine on the image and artificially inflate your bone density reading. A study using both phantoms and human volunteers found that a single 500-milligram calcium tablet overlying a vertebral body could increase the measured bone density of that vertebra by as much as roughly 13 percent, with the effect being more pronounced in people who already had lower bone density.¹ That is a large enough error to shift someone from one diagnostic category to another.

Research confirms that calcium tablet intake can affect lumbar spine measurements within 30 minutes of ingestion, which is why densitometry centers routinely ask patients to abstain before a spine scan.² Most facilities ask you to skip calcium supplements for 24 hours before your appointment, though some say 48 hours. If you forget and take your calcium that morning, mention it to the technologist rather than just going through with the scan silently. They can reschedule or note the potential artifact.

This applies specifically to calcium tablets and chewable calcium supplements. Eating calcium-rich foods like yogurt or cheese before the scan is generally not a concern, because dietary calcium is distributed more diffusely through your digestive system and does not sit as a dense lump the way a tablet does. That said, some clinics give blanket advice to avoid calcium-rich foods as well, so follow whatever instructions your facility provides.

What to Wear and What to Remove

Bone density scans use low-dose X-rays, so anything metal in the scan path will show up on the image and potentially distort your reading. Before the scan, you will be asked to remove belts, underwire bras, and any jewelry around your waist, hips, or spine. Zippers, snaps, and metal buttons can all cause artifacts.

The easiest approach is to wear loose, comfortable clothing with no metal at all. Elastic-waist pants and a cotton T-shirt work well. Many people wear workout clothes. If you show up in jeans with a metal zipper, the technologist will likely ask you to change into a gown for the scan, which adds a few minutes. Facilities usually have gowns available, but dressing simply saves time.

You do not need to fast, and you can take most other medications as usual. The calcium supplement restriction is the main dietary concern. If you take a multivitamin that contains calcium, treat it the same way and skip it the day before.

Mention Recent Contrast Dye or Nuclear Medicine Tests

If you have recently had a CT scan with intravenous contrast dye or a nuclear medicine procedure, tell your doctor or the scheduling staff before your bone density appointment. Contrast agents, particularly barium and iodinated contrast, can linger in your body and interfere with the X-ray readings that the densitometer relies on. Barium swallows are the most common culprit because barium can remain visible in the gastrointestinal tract for days.

The general guidance is to wait at least one to two weeks after a barium study and a few days after a CT with iodinated contrast before scheduling your bone density scan. Nuclear medicine isotopes (used in bone scans, thyroid scans, and cardiac stress tests) can also produce spurious readings. If you have had any of these procedures recently, the scheduling coordinator can advise on the appropriate waiting period.

What Happens During the Scan

A DXA scan (dual-energy X-ray absorptiometry, the standard bone density test) is one of the least eventful medical procedures you will ever have. You lie on a padded table, fully clothed in most cases, and the scanner arm passes over you without touching you. There is no tunnel or enclosed space, so claustrophobia is not a concern. You will not feel any sensation from the X-rays.

The technologist will position you for the specific sites being measured. A standard scan typically covers the lumbar spine and one or both hips, since these are the areas most vulnerable to osteoporotic fractures and most clinically useful for diagnosis. In some cases, the forearm is measured instead or in addition. The whole process usually takes 10 to 20 minutes, including positioning.

You need to stay still during the scan. Even small movements can blur the image and force the technologist to repeat a measurement. This is not difficult for most people, but if you have chronic pain that makes lying flat uncomfortable, let the technologist know so they can work quickly or adjust your position.

Radiation Exposure Is Minimal

One of the most common concerns people have before their first scan is radiation. The dose from a DXA scan is extremely small. A spine and hip scan together deliver a dose that is lower than the average daily natural background radiation in the United States.³ To put that in perspective, a single chest X-ray delivers roughly 10 to 20 times more radiation than a DXA scan, and a CT scan of the abdomen delivers hundreds of times more.

This low dose means the scan is safe for routine screening and for repeat monitoring over the years. You do not need to take any special precautions afterward, and there is no residual radiation to worry about.

Pregnancy and Bone Density Scans

If there is any chance you could be pregnant, tell the technologist before the scan. Although the radiation dose to an embryo or fetus is tiny, pregnancy is still treated as a reason to postpone unless the scan is medically urgent. Research measuring embryo doses during DXA found that the fetal exposure from a spine scan in the first trimester was about 1.7 microgray, and a femur scan delivered about 2.7 microgray. These doses are at least 700 times lower than those from a standard pelvic or thoracolumbar X-ray at any stage of pregnancy.³ The associated cancer risk was estimated at fractions of one case per million exposures.

So while the actual risk is vanishingly small, the standard medical approach is still to avoid any unnecessary radiation during pregnancy. If your doctor believes the scan is important for managing a condition like pregnancy-associated osteoporosis, they can weigh the minimal risk against the clinical benefit.

If You Are a Larger Person

Standard DXA tables have weight limits, typically around 300 to 350 pounds depending on the manufacturer. If you are above that limit, ask the facility about their equipment before your appointment so you are not turned away on the day. Some newer machines accommodate higher weights.

Beyond the weight limit, body size can also affect scan accuracy. If your body extends beyond the edges of the scanning field, a full-body scan is not possible in one pass. Research has explored workarounds like scanning each half of the body separately and combining the data, or measuring regional sites like the thigh or abdomen instead, since these can still provide useful body composition information.⁴ For bone density specifically, the hip and spine can usually still be measured accurately in most larger individuals as long as they fit on the table, since those are targeted rather than whole-body scans.

Things That Can Falsely Raise or Lower Your Results

Even with perfect preparation, certain conditions can distort DXA readings. Knowing about these helps you have a better conversation with your doctor about what your results actually mean.

The most common source of falsely elevated spine readings is degenerative joint disease. Arthritis, bone spurs, and calcified discs in the lumbar spine add extra dense material to the image, making it look like you have more bone than you do. A review in Rheumatology noted that a finding of high bone density on routine DXA scanning is not uncommon and most often reflects degenerative disease rather than genuinely strong bones.⁵ This is especially relevant for older adults, who are the very population being screened for osteoporosis and who are also the most likely to have spinal arthritis.

Other artifacts that can inflate readings include aortic calcification (calcified plaque in the large artery that runs in front of the spine), surgical hardware from prior spinal fusion, and compression fractures that collapse a vertebra and pack its mineral into a smaller area. Conversely, a laminectomy (removal of part of a vertebra) can falsely lower the reading at that level. When the technologist or radiologist sees these issues on the scan, they can exclude the affected vertebrae and report the remaining ones. This is one reason the scan measures multiple vertebrae rather than just one.

Who Should Get Scanned and How Often

Not everyone needs a bone density scan, and understanding the screening guidelines helps you know whether preparation advice even applies to you yet. The U.S. Preventive Services Task Force recommends screening for osteoporosis in all women aged 65 and older, and in postmenopausal women younger than 65 who have one or more risk factors for fracture.⁶ Risk factors include low body weight, a parent who had a hip fracture, smoking, excessive alcohol use, and long-term use of glucocorticoid medications like prednisone.

For men, the evidence is less clear. The USPSTF currently says there is insufficient evidence to recommend for or against routine osteoporosis screening in men.⁶ In practice, many clinicians still order scans for men over 70 or for younger men with specific risk factors like long-term steroid use, low testosterone, or a history of fragility fractures. Medicare covers bone density testing for certain qualifying indications regardless of sex.

If your initial scan is normal, you typically do not need another one for several years. Repeat scans are most useful when enough time has passed for a real change to be detectable beyond the machine’s measurement precision. For most people on treatment or being monitored, that means every two years, though some clinicians extend the interval to five or even ten years for people whose initial results are well within the normal range.

Where on Your Body the Scan Is Done

The gold standard measurement sites are the lumbar spine and the hip, because these are the bones most prone to osteoporotic fractures and have the best-validated diagnostic thresholds. However, peripheral sites like the wrist, heel, or finger are sometimes measured instead, particularly in screening settings that use smaller, portable devices.

Peripheral measurements are useful as a first-pass filter but do not always agree with central (spine and hip) readings. A study comparing wrist, spine, and hip measurements in postmenopausal women found that wrist bone density was significantly lower than both the spine and hip values, while the spine and hip were similar to each other.⁷ This means a wrist scan might flag someone as having low bone density when their spine and hip are actually fine, or the reverse. If a peripheral scan suggests a problem, a follow-up central DXA is usually recommended before making treatment decisions.

The forearm DXA (measured at the distal one-third of the radius) does have a recognized role in specific situations: when the spine or hip cannot be measured due to hardware or severe arthritis, in very large patients whose hip region cannot be properly positioned, or in people with hyperparathyroidism, where cortical bone loss at the wrist is particularly revealing.

Beyond Bone Density Alone

If you are having a DXA scan at a facility with newer software, your results may include something called a trabecular bone score, or TBS. This is not a separate scan. It is a textural analysis of the same lumbar spine DXA image that was already taken, so it requires no extra preparation or radiation on your part.

TBS provides an indirect measure of bone microarchitecture, essentially how the internal scaffolding of your vertebrae is organized. Two people can have identical bone density numbers but very different fracture risks, and TBS helps explain part of that gap. Research has shown that TBS predicts fractures independently of bone density, though reductions in bone density still carry greater fracture risk than reductions in TBS on their own.⁸ TBS is particularly valuable in conditions where bone density alone underestimates fracture risk, such as diabetes, long-term glucocorticoid use, and other endocrine disorders.⁹

Not all facilities calculate TBS, and not all insurance plans cover it, but it is becoming more widely available. You do not need to do anything different to prepare for it. If your doctor has ordered it, it will be computed from the same scan data.

Practical Checklist for the Day Before and Day Of

Pulling together the specifics covered above, here is what to keep in mind:

24 hours before: Stop taking calcium supplements and any multivitamins that contain calcium. Continue all other medications unless your doctor says otherwise.
Day of: Eat normally. There is no need to fast.
Clothing: Wear loose, metal-free clothing. Leave jewelry at home or be prepared to remove it.
Tell the technologist: If you have had a barium study, CT with contrast, or nuclear medicine test in the past two weeks. If you have any metal implants, prior spinal surgery, or joint replacements. If there is any possibility of pregnancy.
During the scan: Lie still. The technologist will position you and do the rest. Expect 10 to 20 minutes on the table.

Getting Your Results

Results are typically reported as a T-score, which compares your bone density to that of a healthy young adult of the same sex. A T-score of minus 1.0 or above is considered normal, between minus 1.0 and minus 2.5 indicates low bone mass (sometimes called osteopenia), and minus 2.5 or below means osteoporosis. Your report may also include a Z-score, which compares you to others of the same age rather than to young adults. The Z-score is mainly used in premenopausal women, men under 50, and children.

If your T-score falls in the osteopenia range, that does not automatically mean you need medication. Your doctor will consider your overall fracture risk, which depends on age, body weight, fracture history, family history, and other factors. Tools like FRAX (a widely used fracture risk calculator) combine bone density with these clinical risk factors to estimate your 10-year probability of a major fracture. That combined risk, not the T-score alone, drives most treatment decisions.

If you are having a repeat scan to monitor changes over time, ask whether the facility is using the same machine brand and model as your previous scan. Different manufacturers’ machines can give slightly different bone density values for the same person, making it harder to detect true changes. Consistency in equipment is one of the easiest ways to make your follow-up scans more useful, and it is something you can actively choose by staying with the same imaging center when possible.