Learn About Bone Density Tests and How They Work

What Are Bone Density Tests and Why They Matter

A bone density test, also called a DEXA scan or DXA scan, measures how much mineral content is in your bones. Bones naturally contain minerals like calcium and phosphorus, which give them strength and hardness. Over time, bones can lose some of these minerals, becoming weaker and more fragile. This condition is called osteoporosis. A bone density test shows whether your bones are storing minerals at healthy levels or if they are losing mineral content faster than normal.

The test produces a score that compares your bone density to healthy young adults. This comparison helps doctors understand your bone health and risk for fractures. About 1 in 3 women over age 70 and 1 in 5 men over age 70 will experience a bone fracture due to osteoporosis, according to the National Institutes of Health. Many people do not know they have weak bones until they break something, which is why bone density testing can be valuable for early detection.

Bone density tests are painless and non-invasive. They use a small amount of radiation—much less than a chest X-ray—to create images of your bones. The procedure typically takes 10 to 30 minutes. Results can help inform conversations with your doctor about whether you need treatment, lifestyle changes, or monitoring over time.

Practical takeaway: Understanding what a bone density test measures helps you prepare for the test and understand what your results mean. The test measures mineral content in bones, not bone strength directly, though the two are related. Ask your doctor if this test might be right for you based on your age, medical history, and other risk factors.

Who Should Consider Getting a Bone Density Test

Bone density testing is recommended for certain groups of people, though not everyone needs one. The U.S. Preventive Services Task Force suggests that all women age 65 and older should have a bone density test. For men, the recommendations are less universal, but testing may be considered starting at age 70 or earlier for men with risk factors.

Younger adults—both men and women—might benefit from bone density testing if they have specific risk factors. These risk factors include a personal history of fractures as an adult, a family history of osteoporosis or fractures, use of certain medications like corticosteroids for long periods, medical conditions that affect bone health such as rheumatoid arthritis or digestive disorders, low body weight, smoking, or excessive alcohol use. Women who have gone through menopause before age 45 may also want to discuss testing with their doctor, since the drop in estrogen during menopause accelerates bone loss.

People taking medications that affect bone density, such as those used to treat cancer, thyroid disease, or autoimmune conditions, should talk with their doctor about whether testing makes sense. Additionally, individuals with a history of falls or balance problems might benefit from knowing their bone density status, as this information can guide prevention strategies.

Practical takeaway: Create a list of your personal risk factors and discuss them with your doctor. You do not need to wait for a certain age to ask about bone density testing if you have multiple risk factors or concerns about your bone health. Your doctor can help you decide whether testing is appropriate for your situation right now.

How Bone Density Tests Work: The Step-by-Step Process

The most common bone density test is the DEXA scan, which stands for dual-energy X-ray absorptiometry. During a DEXA scan, you lie on a padded table while a machine passes over your body. The machine has an arm that moves across your spine, hip, and sometimes your forearm or whole body. This arm emits two different types of X-rays that pass through your bones and soft tissue.

As the X-rays pass through your bones, different amounts of radiation are absorbed depending on how dense the bone is. Denser bones absorb more radiation, while bones that have lost mineral content absorb less. The machine measures the difference and calculates your bone density. The entire scan typically takes 10 to 30 minutes, and you remain fully clothed during the procedure.

Before the test, you may be asked to remove jewelry, eyeglasses, or other metal objects because they can interfere with the images. You do not need to fast or take special preparation steps. The radiation exposure from a DEXA scan is very low—about 1 to 3 microsieverts of radiation. For comparison, the average person receives about 3,000 microsieverts of natural radiation each year from the environment. Pregnant women typically should not have a DEXA scan because of radiation exposure to the developing baby.

The test is completely painless. You will not feel anything during the scan. If you have difficulty lying flat or staying still, inform the technician beforehand. They may be able to adjust the procedure or use alternative positioning. Some imaging centers also offer upright DEXA scans for people who cannot lie down comfortably.

Practical takeaway: Know what to expect during the test so you can feel more relaxed. Plan to arrive 10 to 15 minutes early to complete any paperwork. Wear comfortable clothing without metal fasteners or zippers if possible. The test itself causes no pain or discomfort, and you can return to normal activities immediately afterward.

Understanding Your Bone Density Test Results

Bone density test results are reported using a number called a T-score. Your T-score compares your bone density to the bone density of a healthy 30-year-old adult of the same sex. A T-score of -1.0 or higher is considered normal bone density. A T-score between -1.0 and -2.5 indicates osteopenia, which means your bones are weaker than normal but not yet at the level of osteoporosis. A T-score of -2.5 or lower indicates osteoporosis, meaning your bones are significantly weaker and at higher risk for fractures.

Your doctor may also discuss your Z-score, which compares your bone density to people your same age and sex. The Z-score helps determine whether bone loss is normal for your age or whether something else might be causing faster bone loss than expected. If your Z-score is unusually low, your doctor might investigate other causes of bone loss such as vitamin D deficiency, thyroid problems, or malabsorption disorders.

Results typically include measurements from multiple sites—usually the hip, spine, and sometimes the forearm. Different bones may show different levels of density. For example, you might have normal bone density in your hip but lower density in your spine, or vice versa. Your doctor uses all of this information together to assess your overall bone health.

The report also includes a 10-year fracture risk estimate, which predicts your probability of experiencing a hip or major osteoporotic fracture in the next decade. This number helps guide treatment decisions. For instance, if your 10-year fracture risk is above a certain threshold, your doctor might recommend medication in addition to lifestyle changes.

Practical takeaway: Ask your doctor to explain what your specific T-score and Z-score mean in the context of your age, health history, and risk factors. Do not assume that any result means you must take medication—your doctor will consider your full health picture. Request a copy of your results to share with other healthcare providers and to keep for your records.

What Affects Bone Density and Can You Improve It

Many factors influence bone density throughout your life. Calcium intake is critical because calcium is a main building block of bone. Adults aged 19 to 50 need 1,000 milligrams of calcium daily, while women over 50 and men over 70 need 1,200 milligrams daily. Vitamin D helps your body absorb calcium, making it equally important. Most adults need 600 to 800 international units of vitamin D daily, though requirements may be higher for some people.

Weight-bearing exercise also plays a major role in bone density. Activities like walking, jogging, dancing, hiking, and strength training stimulate bones to maintain or build density. Research shows that people who exercise regularly have higher bone density than those who are sedentary. Exercise does not require a gym membership—activities like gardening, climbing stairs, or playing sports count as weight-bearing activity. Aim for at least 150 minutes of moderate physical activity each week.

Hormonal factors significantly affect bone health. In women, the drop in estrogen during menopause