What A Dexa Scan Can Show?

A DEXA scan is a medical imaging test that measures bone density and body composition. It is the gold standard for diagnosing osteoporosis and assessing fracture risk. The scan uses a low-dose X-ray to measure how much calcium and other minerals are packed into a specific section of bone, most commonly the hip and lower spine.

What Exactly Does a DEXA Scan Measure?

A DEXA scan produces two main types of results: bone density readings and body composition data. For bone health, the scan measures the amount of mineral content in grams per square centimeter of bone. This number is then compared to two reference standards to produce your T-score and Z-score.

The T-score compares your bone density to that of a healthy 30-year-old adult. This is the score doctors use to diagnose osteoporosis. The Z-score compares your bone density to others of your same age, sex, and body size. It helps doctors identify whether bone loss might be caused by something other than normal aging.

For body composition, the same scan can measure total fat mass, lean muscle mass, and bone mass. It shows exactly where fat is distributed in the body, including visceral fat around internal organs. This information is useful for tracking changes in muscle and fat over time, particularly in athletes or people managing metabolic conditions.

How the Scan Works

DEXA stands for Dual-Energy X-ray Absorptiometry. The machine emits two X-ray beams at different energy levels. Each beam is absorbed differently by bone and soft tissue. By comparing how much of each beam passes through the body, the software calculates the density of bone and the amount of fat and lean tissue.

The procedure is simple and painless. You lie flat on a padded table while a scanning arm passes slowly over your body. The scan takes about 10 to 20 minutes depending on whether you are having a bone density test, a body composition test, or both. You remain fully clothed, but you must remove any metal items like belts, zippers, or jewelry that could interfere with the image.

The radiation exposure is very low. A single DEXA scan delivers roughly the same radiation as about one to two hours of natural background radiation you encounter daily from the environment. This is far less than a standard chest X-ray and considerably less than a CT scan.

What the T-Score Numbers Mean

The T-score is the critical number for diagnosing bone health. It is expressed as a standard deviation, which measures how far your bone density is from the average healthy young adult.

• T-score of -1.0 or above: Normal bone density
• T-score between -1.0 and -2.5: Osteopenia, meaning bone density is lower than normal but not yet at osteoporosis level
• T-score of -2.5 or below: Osteoporosis, meaning bone density is significantly low and fracture risk is increased

Each full point drop in T-score roughly doubles your fracture risk. So someone with a T-score of -2.5 has roughly twice the fracture risk of someone with a T-score of -1.5. This is why the test is so valuable — it identifies increased risk before a fracture occurs.

A diagnosis of osteopenia does not mean you will definitely develop osteoporosis. It means your bone density is below average and you should discuss prevention strategies with your doctor. Many people with osteopenia never progress to osteoporosis.

Who Should Get a DEXA Scan

The U.S. Preventive Services Task Force recommends screening for osteoporosis in all women aged 65 and older. Women younger than 65 should consider screening if they have risk factors such as early menopause, a history of fractures, long-term steroid use, or a family history of osteoporosis.

Men are not routinely screened unless they have specific risk factors. These include age over 70, low body weight, smoking, excessive alcohol use, long-term corticosteroid use, or a prior fracture after age 50. Men with prostate cancer receiving hormone therapy should also discuss screening with their doctor.

Certain medical conditions warrant earlier or more frequent testing. These include rheumatoid arthritis, hyperthyroidism, hyperparathyroidism, chronic kidney disease, and conditions that cause malabsorption such as celiac disease or inflammatory bowel disease. If you take medications that affect bone density — such as glucocorticoids, certain anticonvulsants, or aromatase inhibitors — your doctor may order a baseline scan.

For body composition analysis, DEXA is increasingly used by athletes and people managing weight or metabolic conditions. It provides precise measurements of lean mass and fat mass that standard scales cannot offer. However, body composition testing is not a routine medical screening — it is typically done at specialized facilities and may not be covered by insurance.

How Often Should You Repeat the Scan

The frequency of follow-up scans depends on your initial results and your treatment plan. For someone with normal bone density, repeating the scan every 10 to 15 years is generally sufficient. For someone with osteopenia, follow-up every 2 to 5 years is typical.

If you are taking medication for osteoporosis, your doctor may order a follow-up scan every 1 to 2 years to assess whether the treatment is working. Bone density changes slowly, so more frequent testing rarely provides useful information. Two years is usually the minimum interval to detect a meaningful change.

Consistency matters for accurate comparisons. Try to have follow-up scans done on the same machine or at the same facility whenever possible. Different machines can produce slightly different readings, which can make it difficult to tell whether a change is real or just measurement variation.

What a DEXA Scan Cannot Show

A DEXA scan measures bone quantity, not bone quality. Two people can have identical bone density scores but very different fracture risks. Bone quality refers to the internal structure, microarchitecture, and collagen framework of bone — none of which DEXA can assess. This is why some people with normal bone density still experience fractures and others with low density do not.

The scan also cannot diagnose the cause of bone loss. If your results show low bone density, your doctor will need blood tests and a clinical evaluation to determine why. Common causes include vitamin D deficiency, calcium deficiency, thyroid disorders, and hormonal changes, but the scan itself provides no information about these underlying factors.

DEXA cannot detect stress fractures, bone infections, or tumors. It is not a diagnostic tool for bone pain. If you have localized bone pain, an X-ray, MRI, or bone scan would be more appropriate imaging tests.

Preparing for Your Scan

There is minimal preparation required. Avoid taking calcium supplements for 24 hours before your scan, because undigested calcium in your digestive tract can interfere with the accuracy of the spine measurement. Wear comfortable clothing without metal fasteners. You may be asked to change into a hospital gown.

Inform the technologist if you have had a recent barium study or a nuclear medicine scan. These procedures use contrast material that can interfere with DEXA readings. If you have had spinal surgery or metal implants in your spine or hips, tell the technologist — this affects which areas can be accurately measured.

If you are pregnant or think you might be pregnant, tell your doctor before the scan. Although radiation exposure is very low, DEXA is not performed during pregnancy unless there is a strong medical reason.

What to Do With Your Results

Your doctor will explain your results and what they mean for your specific situation. If your bone density is normal, continue with preventive measures such as adequate calcium and vitamin D intake, weight-bearing exercise, and avoiding smoking and excessive alcohol.

If you have osteopenia or osteoporosis, your doctor will discuss treatment options. These may include lifestyle changes, supplements, or prescription medications. The decision to start medication depends on your T-score, your age, your fracture history, and other risk factors — not just the scan result alone.

Fracture risk assessment tools, such as the FRAX score, combine your DEXA results with other clinical factors to estimate your 10-year probability of major fracture. This gives a more complete picture than the T-score alone. Your doctor may use this tool to guide treatment decisions.

DEXA vs. Other Bone Density Tests

DEXA is the most widely used and best-validated method for measuring bone density. Peripheral DEXA measures bone density in the wrist, heel, or finger using a smaller portable device. These are useful for screening but are less accurate than central DEXA and cannot be used to diagnose osteoporosis definitively.

Quantitative computed tomography (QCT) measures bone density in three dimensions and can separate cortical bone from trabecular bone. It provides more detailed information but uses higher radiation doses and is more expensive. It is typically reserved for research or specific clinical situations.

Ultrasound of the heel is sometimes used as a screening tool because it is quick and radiation-free. However, it is not as accurate as DEXA and is not recommended as a substitute for central DEXA when making treatment decisions.