Bone Density Scan (DEXA): Complete Guide to Osteoporosis Testing

What Is a Bone Density Scan (DEXA)?

A DEXA scan (Dual-Energy X-ray Absorptiometry, also written as DXA) is a medical imaging test that measures bone mineral density using two low-dose X-ray beams at different energy levels. The scan determines how dense and strong your bones are, helping diagnose osteoporosis and predict your risk of fractures.

Bone density scanning is the most reliable method available for measuring bone health. The test works by passing two X-ray beams with different energy levels through the bone. Because bone absorbs more radiation than soft tissue, the scanner can calculate exactly how much mineral content is present in your bones. The areas most commonly scanned are the lower spine (lumbar vertebrae) and the hip, as these are the most reliable sites for assessing overall bone health and predicting fracture risk.

The technology behind DEXA scanning was developed in the 1980s and has become the gold standard for osteoporosis diagnosis worldwide. The test is endorsed by the World Health Organization (WHO), the International Society for Clinical Densitometry (ISCD), and major medical organizations globally. Unlike other imaging methods, DEXA provides precise numerical measurements that can be tracked over time to monitor bone health changes.

Understanding your bone density is crucial because osteoporosis often has no symptoms until a fracture occurs. By the time someone breaks a bone from a minor fall or even normal activities like bending or coughing, significant bone loss has already occurred. DEXA scanning allows healthcare providers to identify bone weakness before fractures happen, enabling preventive treatment that can significantly reduce fracture risk.

How DEXA Technology Works

The DEXA scanner uses a technique called dual-energy X-ray absorptiometry, which sounds complex but works on a straightforward principle. Two X-ray beams at different energy levels pass through the body simultaneously. Bone tissue absorbs these two energy levels differently than soft tissue does. A computer then analyzes the absorption patterns to calculate the exact mineral content of the bone being measured.

This dual-energy approach is what makes DEXA so accurate. By comparing how the two different energy beams are absorbed, the technology can distinguish between bone, fat, and lean tissue with remarkable precision. The result is a bone mineral density (BMD) measurement expressed in grams per square centimeter (g/cm²), which is then compared to reference populations to generate your T-score and Z-score.

Types of DEXA Scanners

There are two main types of DEXA machines used in clinical practice. Central DEXA scanners are large machines that measure bone density in the spine and hip—these are the standard devices used in hospitals and imaging centers, and they provide the most accurate measurements. Peripheral DEXA scanners are smaller, portable devices that measure bone density in the heel, finger, or wrist. While peripheral devices are convenient for screening purposes, they cannot diagnose osteoporosis and their results don't always correlate with central skeletal measurements.

Who Should Get a Bone Density Scan?

Bone density testing is recommended for all women aged 65 and older, all men aged 70 and older, postmenopausal women under 65 with risk factors, adults who have had fractures after age 50, people taking medications that cause bone loss (like corticosteroids), and those with medical conditions affecting bone health.

The decision to undergo bone density testing depends on your age, sex, and individual risk factors for osteoporosis and fractures. Major medical organizations have established clear guidelines to help healthcare providers determine who should be screened. These recommendations are based on extensive research showing which populations benefit most from early detection and treatment of low bone density.

For women, the risk of osteoporosis increases dramatically after menopause due to declining estrogen levels. Estrogen plays a crucial protective role in maintaining bone density, and its decline can lead to rapid bone loss in the years following menopause. This is why screening recommendations often focus on postmenopausal women, particularly those with additional risk factors. Men also develop osteoporosis, though typically about 10 years later than women on average, which is why screening recommendations for men begin at age 70.

Beyond age-based screening, many medical conditions and lifestyle factors significantly increase osteoporosis risk. These include a family history of osteoporosis or hip fracture, low body weight, smoking, excessive alcohol consumption, certain medications, and various chronic diseases. Healthcare providers use clinical judgment along with formal risk assessment tools to determine the appropriate timing for bone density testing in individuals who don't meet age-based criteria.

Standard Screening Recommendations

According to the International Society for Clinical Densitometry (ISCD) and other major organizations, the following groups should undergo bone density testing:

• Women aged 65 and older: All women should be screened regardless of risk factors
• Men aged 70 and older: All men should be screened regardless of risk factors
• Postmenopausal women under 65: If they have one or more risk factors for osteoporosis
• Men aged 50-69: If they have clinical risk factors for fracture
• Adults with fragility fractures: Anyone who has broken a bone from minimal trauma after age 50
• Adults with conditions causing bone loss: Including rheumatoid arthritis, chronic kidney disease, or eating disorders
• Adults taking medications affecting bone: Particularly glucocorticoids (prednisone), aromatase inhibitors, or androgen deprivation therapy

Risk Factors That Warrant Earlier Testing

Several factors increase your risk of osteoporosis and may prompt your doctor to recommend bone density testing before the standard screening ages. Understanding these risk factors helps you have informed conversations with your healthcare provider about whether and when testing is appropriate for you.

Genetic and family history factors play a significant role. If a parent, especially your mother, had a hip fracture or was diagnosed with osteoporosis, your risk is substantially higher. Certain ethnic backgrounds also influence risk—Caucasian and Asian women have higher rates of osteoporosis than women of African or Hispanic descent, though the disease affects all populations.

Lifestyle factors that increase risk include smoking (which directly damages bone cells), excessive alcohol consumption (more than 3 drinks daily), low calcium and vitamin D intake, and sedentary lifestyle (weight-bearing exercise strengthens bones). Low body weight, defined as a body mass index below 20, is also a significant risk factor because heavier individuals have greater mechanical loading on their bones and more protective fat tissue that produces estrogen.

How Do I Prepare for a DEXA Scan?

DEXA scans require minimal preparation. You don't need to fast or change your routine. Before the test, remove jewelry and metal objects near the scan area, and avoid calcium supplements for 24-48 hours if instructed. Inform your doctor if you've had recent barium contrast studies or nuclear medicine tests, as these can interfere with results.

One of the advantages of DEXA scanning is its simplicity and convenience. Unlike many medical imaging procedures, bone density testing doesn't require fasting, special diets, or significant lifestyle modifications beforehand. You can eat normally, drink fluids, and take most medications as usual on the day of your scan. However, there are a few simple preparations that will ensure the most accurate results.

The most important preparation involves calcium supplements. If you take calcium supplements, your doctor may ask you to avoid taking them for 24 to 48 hours before the scan. Calcium supplements can sometimes interfere with the accuracy of the bone density measurement, particularly if taken shortly before the test. However, calcium in food is not a concern—you can eat your regular diet including dairy products and other calcium-rich foods without affecting the scan results.

On the day of your appointment, wear comfortable, loose-fitting clothing without metal fasteners, zippers, or buttons in the areas being scanned (lower back and hip region). Many facilities will offer you a hospital gown to wear, but if your clothing has no metal in the scan area, you may be able to keep it on. This can make the experience more comfortable and efficient.

What to Remove Before the Scan

Metal objects can interfere with X-ray absorption and create artifacts on the scan image, potentially affecting the accuracy of your results. Before your DEXA scan, you'll need to remove:

• Belts with metal buckles
• Jewelry in the abdominal or hip area (necklaces typically don't need removal)
• Coins or keys in pockets
• Body piercings in the scan area if possible
• Underwire bras (or you may be asked to change into a gown)

Important Information to Tell Your Healthcare Provider

Before scheduling or undergoing your DEXA scan, inform your healthcare provider about certain circumstances that might affect the timing or interpretation of your test. Recent barium contrast studies (used for gastrointestinal imaging) or nuclear medicine procedures (such as bone scans or certain heart tests) can interfere with DEXA accuracy. Your doctor may recommend waiting 10-14 days after these procedures before having a bone density scan.

Also tell your provider if you have any implanted medical devices, such as a pacemaker or spinal hardware from previous surgery. While these devices don't prevent DEXA scanning, the technologist may need to adjust the scan area or use specific protocols to ensure accurate measurements. Similarly, if you've had joint replacement surgery (hip or knee replacement), the metal implant will affect measurements on that side, so the other hip may be used for assessment.

How Does the DEXA Scan Procedure Work?

During a DEXA scan, you lie flat on a padded table while a scanning arm passes slowly above your lower spine and hip. The machine emits very low-dose X-rays to measure bone density. The procedure takes 10-20 minutes, is completely painless, and requires you to remain still during scanning. You can breathe normally throughout.

The DEXA scanning procedure is remarkably straightforward and comfortable for patients. When you arrive at the imaging facility, a trained technologist will guide you through the process. After removing any metal objects and changing into a gown if necessary, you'll be asked to lie on your back on a padded examination table. The table is similar to those used for other X-ray procedures but is specifically designed for bone density scanning.

Once you're positioned on the table, the technologist will help you get into the correct position for accurate measurements. For the spine scan, a cushioned block may be placed under your knees to flatten your lower back against the table, which helps produce clearer images of the lumbar vertebrae. You'll need to remain as still as possible during each scan, though you can breathe normally—holding your breath is not required.

The DEXA machine consists of two main components: the table you lie on and a scanning arm positioned above you. During the scan, this arm moves slowly along your body, passing over the areas being measured. Unlike tunnel-type scanners used for CT or MRI, DEXA machines are open and don't enclose you, making the experience comfortable even for people who feel anxious in enclosed spaces.

The Scanning Sequence

A standard DEXA examination includes scans of two areas: the lumbar spine (lower back) and one or both hips. The spine scan typically comes first. The scanning arm moves from your head toward your feet, measuring the bone density of your lumbar vertebrae (L1 through L4). This portion usually takes 30-60 seconds.

For the hip scan, the technologist will position your leg in a special brace or support that rotates your foot inward. This rotation positions the femur (thigh bone) correctly for accurate measurement of the femoral neck and total hip area. The hip scan also takes about 30-60 seconds per side. If both hips are being measured, you'll be repositioned between scans.

Throughout the procedure, you won't feel anything from the X-rays themselves. The most common sensation patients report is slight discomfort from lying still on the table, particularly if they have back pain. If you experience significant discomfort, inform the technologist—small position adjustments can often help without affecting scan quality.

Additional Scan Sites

In some cases, your healthcare provider may request measurements at additional body sites. The forearm (specifically the radius bone near the wrist) is sometimes measured when spine or hip measurements cannot be obtained accurately—for example, in patients with significant spinal arthritis or bilateral hip replacements. Some specialized protocols also include whole-body composition scans that measure total body fat, lean mass, and bone mineral content.

What Happens After My Bone Density Scan?

After a DEXA scan, you can immediately return to all normal activities with no restrictions. There's no recovery period needed. Results are typically available within a few days to two weeks and will be interpreted by a radiologist or your ordering physician. Your doctor will discuss the results and any recommended next steps with you.

One of the significant advantages of DEXA scanning is that there are absolutely no after-effects or recovery time required. The low-dose radiation used in the scan doesn't cause any physical sensations, and there are no medications or contrast agents that might affect how you feel afterward. You can drive yourself home, return to work, exercise, and eat normally immediately after leaving the imaging facility.

The images from your scan will be analyzed by a qualified healthcare professional, typically a radiologist or a physician trained in bone densitometry. The analysis involves identifying specific anatomical regions of interest on the scan images and calculating the bone mineral density in those regions. Advanced software performs most of this analysis automatically, but a trained eye is needed to verify accuracy and identify any anatomical variations or artifacts that might affect the results.

Results are generally available within a few days to two weeks, depending on the facility and how quickly your healthcare provider reviews them. Some facilities offer same-day preliminary results, while others send formal reports to your ordering physician who then contacts you to discuss the findings. When you schedule your scan, ask about the typical timeline for receiving results at that facility.

Follow-Up Appointments

After receiving your DEXA results, your healthcare provider will want to discuss them with you, either during a scheduled follow-up appointment or through a phone call or patient portal message. This discussion is important because bone density is just one factor in assessing your bone health and fracture risk. Your provider will interpret the results in the context of your overall health, risk factors, and treatment goals.

If your results show normal bone density, your doctor may recommend lifestyle measures to maintain bone health (adequate calcium, vitamin D, and weight-bearing exercise) and schedule a follow-up scan in several years. If results show osteopenia or osteoporosis, additional evaluation and treatment options will be discussed, potentially including medications to strengthen bones and reduce fracture risk.

What Do DEXA Scan Results Mean?

DEXA results are reported as T-scores, comparing your bone density to a healthy 30-year-old adult. A T-score of -1.0 or higher is normal. A T-score between -1.0 and -2.5 indicates osteopenia (low bone mass). A T-score of -2.5 or lower indicates osteoporosis. Each 1.0 decrease in T-score approximately doubles your fracture risk.

Understanding your DEXA results empowers you to participate actively in decisions about your bone health. The primary measurement reported is your T-score, which compares your bone density to that of a healthy young adult at peak bone mass (typically around age 30). This comparison is used because peak bone mass represents the strongest bones will ever be, providing a consistent reference point for assessment.

The T-score is expressed as a standard deviation from the young adult mean. A T-score of 0 means your bone density is exactly average for a healthy young adult. Positive values indicate denser-than-average bones, while negative values indicate lower density. The further your T-score deviates from zero in the negative direction, the weaker your bones and the higher your fracture risk.

The World Health Organization established the diagnostic criteria for osteoporosis based on T-scores in 1994, and these definitions remain the international standard today. It's important to understand that these are diagnostic thresholds, not absolute boundaries—someone with a T-score of -2.4 is at nearly the same risk as someone with -2.6, even though one technically meets the osteoporosis definition and the other doesn't.

T-Score Categories Explained

Understanding Z-Scores

Your DEXA report will also include a Z-score, which compares your bone density to what's expected for someone of your same age, sex, and sometimes ethnicity. While T-scores are used for diagnosis in postmenopausal women and men over 50, Z-scores are more relevant for younger adults and can help identify whether bone loss is unusual for your age.

A Z-score below -2.0 is considered "below the expected range for age" and may prompt your healthcare provider to investigate underlying causes of bone loss, such as hormonal disorders, vitamin D deficiency, celiac disease, or medication effects. This is particularly important in premenopausal women or men under 50, where osteoporosis is less common and often indicates a secondary cause.

FRAX Fracture Risk Assessment

Modern osteoporosis management goes beyond just looking at bone density numbers. The FRAX tool (Fracture Risk Assessment Tool) combines your bone density measurement with other risk factors to calculate your 10-year probability of having a major osteoporotic fracture (spine, hip, forearm, or shoulder) or hip fracture specifically.

FRAX considers factors including age, sex, weight, height, previous fractures, parental hip fracture history, current smoking, glucocorticoid use, rheumatoid arthritis, secondary osteoporosis, and alcohol intake. The resulting percentage helps guide treatment decisions—generally, treatment is recommended when 10-year hip fracture risk exceeds 3% or major osteoporotic fracture risk exceeds 20%, though thresholds vary by country and clinical guidelines.

How Often Should I Get a Bone Density Scan?

The frequency of DEXA scanning depends on your initial results and treatment status. People with normal bone density may wait 10-15 years before rescanning. Those with osteopenia typically repeat scans every 1-5 years depending on risk factors. People on osteoporosis treatment should have follow-up scans every 1-2 years to monitor response.

Once you've had an initial bone density measurement, the timing of follow-up scans depends on your results, risk factors, and whether you're receiving treatment. The goal of repeat scanning is to detect significant changes in bone density that might alter your management—either progression of bone loss that warrants starting treatment, or response to treatment that confirms it's working effectively.

For individuals with normal bone density (T-score above -1.0), frequent rescanning is generally not necessary. Research suggests that most people with normal results can safely wait 10-15 years before their next scan, unless they develop new risk factors or symptoms suggestive of bone loss. More frequent monitoring in low-risk individuals leads to unnecessary healthcare costs without improving outcomes.

The interval is shorter for those with osteopenia because they're at higher risk of progressing to osteoporosis. Guidelines typically recommend repeat scanning every 1-5 years for this group, with the exact interval based on how close the T-score is to the osteoporosis threshold and the presence of other risk factors. Someone with a T-score of -2.4 will likely be monitored more frequently than someone with -1.2.

Monitoring Treatment Response

For people receiving osteoporosis treatment, follow-up DEXA scans serve a different purpose: confirming that treatment is working. Most osteoporosis medications take 6-12 months to show measurable effects on bone density, and the typical change expected is only 2-5% per year. Because of this, scans performed too frequently may not show detectable changes and can be misleading.

Most guidelines recommend follow-up scans 1-2 years after starting treatment, then every 2 years thereafter if bone density is stable or improving. If results show continued bone loss despite treatment, your healthcare provider may investigate causes of treatment failure, such as poor medication adherence, vitamin D deficiency, or secondary conditions affecting bone metabolism.

Is a Bone Density Scan Safe?

DEXA scans are extremely safe. The radiation exposure is very low—approximately 1-6 microsieverts, which is about 1/10th of a chest X-ray and equivalent to a few hours of natural background radiation. The only absolute contraindication is pregnancy. The benefits of identifying osteoporosis far outweigh the minimal radiation risk.

Bone density scanning is one of the safest medical imaging procedures available. The radiation dose from a DEXA scan is remarkably low—typically between 1 and 6 microsieverts depending on the machine and protocol used. To put this in perspective, the average person receives about 2,400 microsieverts of radiation annually just from natural background sources (cosmic rays, radon gas, and naturally occurring radioactive materials in the environment). A single DEXA scan adds only a tiny fraction—less than one day's worth—of this natural exposure.

The radiation from DEXA is also much lower than many common medical imaging procedures. A standard chest X-ray delivers approximately 20-100 microsieverts, making it 10-50 times higher than a DEXA scan. A CT scan of the abdomen, which involves much higher doses, delivers about 10,000 microsieverts or more. The low radiation dose is one reason DEXA can be safely repeated periodically for monitoring purposes.

There are no known harmful effects from the radiation doses used in DEXA scanning. The theoretical cancer risk from such low exposure is so small that it cannot be measured or distinguished from background rates. For comparison, the radiation from flying across the country (from cosmic radiation at high altitude) is similar to having a DEXA scan.

Contraindications and Precautions

The only absolute contraindication to DEXA scanning is pregnancy. Although the radiation dose is very low, any unnecessary radiation exposure should be avoided during pregnancy. If there's any possibility you might be pregnant, inform the facility before your scan. Many imaging centers have policies requiring pregnancy tests for women of childbearing age.

Breastfeeding is not a contraindication—the X-rays used in DEXA do not affect breast milk composition or safety. Nursing mothers can breastfeed normally before and after a bone density scan without any waiting period or need to pump and discard milk.

Certain factors may affect scan accuracy but don't represent safety concerns. Recent barium contrast from gastrointestinal studies or radioactive tracers from nuclear medicine procedures can interfere with measurements. Spinal hardware, severe scoliosis, or significant degenerative changes may make spine measurements unreliable. In these cases, alternative measurement sites can be used.

Can I Have a Bone Density Scan During Pregnancy?

DEXA scans should not be performed during pregnancy because they use X-ray radiation. Since there are no approved osteoporosis treatments safe for use during pregnancy, testing is deferred until after delivery. If you're breastfeeding, the scan is completely safe and can be performed without any special precautions.

Pregnancy is the one situation where bone density scanning is routinely postponed. While the radiation dose from DEXA is extremely low, medical guidelines recommend avoiding any non-essential radiation exposure during pregnancy. The developing fetus is more sensitive to radiation than adults, and although the actual risk from a DEXA scan would be negligible, the precautionary principle applies when the test isn't urgently needed.

From a practical standpoint, there's another reason DEXA scanning isn't performed during pregnancy: even if osteoporosis were diagnosed, treatment couldn't be initiated. The medications used to treat osteoporosis—including bisphosphonates, denosumab, and other bone-building drugs—are not approved for use during pregnancy due to potential risks to fetal skeletal development. Therefore, testing serves no immediate clinical purpose during pregnancy.

If bone health concerns exist before or during pregnancy, healthcare providers typically recommend optimizing calcium and vitamin D intake, maintaining appropriate physical activity, and deferring formal bone density assessment until after delivery. Pregnancy itself can cause some temporary changes in bone density, which typically normalize after weaning if breastfeeding occurs.

Bone Health During and After Pregnancy

Pregnancy and breastfeeding place significant demands on maternal calcium stores. The developing fetus requires substantial calcium for skeletal formation, particularly during the third trimester. If dietary calcium is insufficient, the body mobilizes calcium from maternal bones to meet fetal needs. During breastfeeding, calcium continues to transfer to the baby through breast milk.

The good news is that most bone loss during pregnancy and lactation is temporary. Studies show that bone density typically returns to pre-pregnancy levels within 12-18 months after weaning, even without specific treatment. However, women who had multiple closely-spaced pregnancies, those with very low calcium intake, or those with pre-existing bone health concerns may benefit from monitoring after completing their families.

What Treatments Are Available for Low Bone Density?

Treatment for osteoporosis includes lifestyle measures (calcium, vitamin D, weight-bearing exercise, fall prevention) and medications. Drug options include bisphosphonates (alendronate, risedronate), denosumab, hormone therapy, and bone-building medications (teriparatide, romosozumab). Treatment selection depends on fracture risk, other health conditions, and patient preferences.

If your DEXA scan reveals low bone density, various treatment options can help prevent fractures and maintain bone health. Treatment decisions are individualized based on your degree of bone loss, fracture history, other medical conditions, and personal preferences. The goal of osteoporosis treatment is primarily to prevent fractures, which can cause significant pain, disability, and in the case of hip fractures, increased mortality risk.

All osteoporosis treatment plans should include foundational lifestyle measures. Adequate calcium intake (1000-1200 mg daily for most adults, preferably from food sources) provides the building blocks bones need. Vitamin D (600-800 IU daily, or more if deficient) is essential for calcium absorption. Weight-bearing exercise (walking, jogging, dancing, stair climbing) and resistance training stimulate bone formation and improve muscle strength. Fall prevention strategies become increasingly important as they address the immediate cause of most fractures.

When medication is indicated, several classes of drugs have proven effective at reducing fracture risk. The choice among them depends on factors including the severity of bone loss, whether you've had fractures, other health conditions, and practical considerations like dosing preference (daily pills, weekly pills, monthly infusions, or twice-yearly injections).

Medication Options

Bisphosphonates are the most commonly prescribed osteoporosis medications and include alendronate (Fosamax), risedronate (Actonel), ibandronate (Boniva), and zoledronic acid (Reclast). These drugs work by slowing bone breakdown, allowing bone-building processes to keep pace. They reduce spine and hip fracture risk by 40-70% over three years. Oral bisphosphonates must be taken on an empty stomach with water, followed by remaining upright for 30-60 minutes to prevent esophageal irritation.

Denosumab (Prolia) is a biologic medication given as an injection under the skin every six months. It works by blocking a protein involved in bone breakdown. Denosumab is particularly useful for patients who can't take bisphosphonates or have kidney impairment. Unlike bisphosphonates, its effects wear off after stopping, requiring transition to another medication.

Anabolic agents actually build new bone rather than just preventing loss. Teriparatide (Forteo) and abaloparatide (Tymlos) are daily injections that stimulate bone formation. Romosozumab (Evenity) is a monthly injection that both builds bone and reduces bone breakdown. These medications are typically reserved for severe osteoporosis or after other treatments have failed, as they're more expensive and have usage duration limits.

Frequently Asked Questions About Bone Density Scans