Learn How Bone Density Tests Work and Results

What Bone Density Tests Measure and Why They Matter

Bone density tests, also called DXA scans or DEXA scans, measure how much mineral content is packed into your bones. Think of bone as a sponge—bones contain solid material and tiny air spaces. The more mineral content in those spaces, the denser and stronger your bones are. A bone density test uses X-rays to take pictures of your skeleton and calculate the amount of calcium and other minerals present.

These tests matter because they help identify whether your bones are becoming weaker, a condition called osteoporosis. According to the National Osteoporosis Foundation, about one in three women over age 70 and one in five men over age 70 will break a bone due to osteoporosis in their remaining lifetime. Bone density tests can catch bone loss before fractures happen, giving you time to take steps that might slow or stop further weakening.

The test is particularly important for certain groups. Women going through or past menopause face faster bone loss due to dropping estrogen levels. Men over 70 also experience increased bone loss. People taking certain medications like corticosteroids, those with a family history of osteoporosis, or individuals with conditions affecting bone health should consider getting tested. The test provides a clear picture of your current bone strength, which can guide decisions about diet, exercise, and medical treatment.

Bone density testing has been used since the 1980s and is considered the gold standard for measuring bone strength. The procedure takes only 10 to 30 minutes, involves no needles or injections, and exposes you to very small amounts of radiation—less than you receive from a day of natural sunlight. Understanding what the test measures helps you understand why your doctor might recommend one and what the results mean for your health.

Practical takeaway: Bone density tests measure mineral content in your bones using low-dose X-rays and can detect bone loss before fractures occur. Ask your doctor whether this test is right for you based on your age, medical history, and risk factors.

How Bone Density Tests Are Performed

The most common bone density test is called a DXA scan, which stands for dual-energy X-ray absorptiometry. During the procedure, you lie on a padded table while a scanning arm moves slowly over your body, usually focusing on your hip, spine, and sometimes your forearm. The scan produces images that a computer analyzes to calculate your bone density. The entire process is painless and takes between 10 and 30 minutes depending on which bones are being tested.

Before your scan, you'll be asked to remove any metal objects like jewelry, belt buckles, or buttons, since metal can interfere with the X-ray images. You don't need to change into a hospital gown—you can wear your regular clothes as long as they don't contain metal. You may be asked to wear a hospital gown only if your clothing has metal zippers or snaps. Some facilities ask you to remove your shoes and may have you lie on the scanning table with your legs supported by a foam box to keep them still and positioned correctly.

During the actual scan, the X-ray source and detector move slowly across your body. You'll need to stay still and may be asked to hold your breath for a few seconds during the spine portion. The X-ray exposure is very minimal—a DXA scan uses about one-tenth the radiation of a chest X-ray. The technician operating the machine will be in the room with you but may step behind a protective barrier during the actual scanning. Many facilities allow you to bring headphones to listen to music or an audiobook during the scan.

Some newer machines use a different technology called quantitative computed tomography (QCT), which uses a CT scanner to measure bone density. QCT scans provide a three-dimensional picture and can be particularly useful for people with spinal problems or arthritis, but they deliver higher radiation doses than DXA scans. Another option, called peripheral DXA, uses a smaller machine to scan your forearm, hand, or heel and takes only 1 to 3 minutes. These peripheral scans are useful for initial screening but typically cannot be used to monitor changes over time.

Practical takeaway: Bone density testing is a quick, painless procedure requiring you to lie still on a table while an X-ray scanner moves over your body. Remove metal objects before your appointment and wear comfortable, metal-free clothing. The radiation exposure is minimal and safe.

Understanding Your Bone Density Test Results

Bone density test results are reported using a number called a T-score. This score compares your bone density to the bone density of a healthy young 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 low bone mass, a condition called osteopenia. A T-score of -2.5 or lower indicates osteoporosis, meaning your bones are significantly weaker and fracture risk is higher.

To understand this better, think of the T-score as a comparison. A T-score of 0 means your bones are as dense as a young adult's. A T-score of -1 means your bone density is 10 percent lower than a young adult's. A T-score of -2.5 means your bone density is 25 percent lower. The lower the number, the weaker your bones compared to the reference standard. Results typically show separate scores for different areas of your body, such as your hip, spine, and forearm, because bone density can vary by location.

Your doctor may also calculate a 10-year fracture risk using your T-score and other factors through a tool called FRAX (Fracture Risk Assessment Tool). This tool considers your age, sex, weight, height, previous fractures, smoking status, alcohol use, and family history of hip fractures to estimate your probability of breaking a bone in the next 10 years. For example, a 65-year-old woman with a T-score of -1.5 and no other risk factors might have a 10-year risk of hip fracture around 3 percent, while the same woman who smokes and had a previous fracture might have a 15 percent risk.

It's important to remember that a bone density score is only part of the picture. Someone with normal bone density can still break bones if they fall, and someone with low bone density doesn't automatically have fractures. Your doctor considers your overall health, balance, fall risk, and other medical conditions when deciding on treatment. Results should be discussed with your healthcare provider, who can explain what your specific numbers mean and what steps might be helpful for your situation.

Practical takeaway: T-scores compare your bone density to young adult standards. Normal is -1.0 or higher, osteopenia (low bone mass) is between -1.0 and -2.5, and osteoporosis is -2.5 or lower. Your doctor may calculate your 10-year fracture risk using additional factors beyond just your bone density.

Who Should Have Bone Density Testing and When

Medical organizations have specific recommendations about who should get bone density testing. The U.S. Preventive Services Task Force recommends bone density screening for all women age 65 and older and for postmenopausal women under 65 who have risk factors for osteoporosis. The American Academy of Family Physicians recommends screening all women over 65 and men over 70. For men between 50 and 69, screening may be considered if they have risk factors.

Certain medical conditions make testing more important regardless of age. People with rheumatoid arthritis, chronic kidney disease, celiac disease, or inflammatory bowel disease often have weaker bones. Those taking medications that affect bone health, such as corticosteroids used for asthma, rheumatoid arthritis, or lupus, may benefit from testing. People who have had an organ transplant or are being treated for cancer should discuss testing with their doctor, as cancer treatments and transplant medications can affect bone density.

A personal or family history of osteoporosis is another reason for testing. If your mother or father broke a hip bone, your own fracture risk is higher. People who have broken a bone as an adult, especially from a minor fall, should be tested. A history of eating disorders, which can lead to nutritional deficiencies, increases bone loss risk. Excessive alcohol use (more than three drinks daily for men or two for