The bone density scan is the standard test

A doctor diagnoses osteoporosis using a bone density scan, also called a DXA scan or DEXA scan. This test measures how much mineral is packed into your bones and compares your bone density to that of a healthy young adult. The scan takes about 10 to 30 minutes, uses a very small amount of radiation (less than a chest X-ray), and causes no pain.

During the scan, you lie on a table while a machine passes over your bones. The machine most often checks your hip, spine, and sometimes your forearm—the places where osteoporosis breaks bones most often. You stay fully clothed and do not need to undress or change into a hospital gown.

Key Takeaways

  • A bone density scan (DXA) is the only test that diagnoses osteoporosis; blood tests and X-rays cannot detect it early.
  • The scan produces a T-score that compares your bone density to a healthy young adult's, and your score determines whether you have osteoporosis, low bone density, or normal bones.
  • Most people over 50 should have at least one bone density scan, and your doctor will tell you how often you need repeat scans based on your results and risk factors.
  • You do not need to fast, stop medications, or prepare in any special way before a bone density scan.

What the T-score means

After your scan, you receive a report with a number called a T-score. This number tells you how your bone density compares to a healthy 30-year-old's bones. A T-score of -1.0 or higher is considered normal. A score between -1.0 and -2.5 means you have low bone density (sometimes called osteopenia). A score of -2.5 or lower means you have osteoporosis.

The lower your T-score, the weaker your bones are and the higher your risk of breaking a bone from a fall or minor injury. Your doctor uses your T-score along with other risk factors—such as your age, sex, and family history—to decide whether you need treatment to strengthen your bones.

Who should have a bone density scan

The U.S. Preventive Services Task Force recommends that all women age 65 and older have a bone density scan. Women between 50 and 64 should talk to their doctor about whether a scan makes sense for them, based on their risk factors. Men age 70 and older should also be scanned.

You may need a scan earlier if you have risk factors such as a family history of osteoporosis, a previous broken bone, long-term use of certain medications (like steroids), or conditions that affect bone health. Your doctor can tell you whether a scan is right for you.

How often you need repeat scans

If your first scan shows normal bone density, you may not need another scan for 10 years, depending on your age and risk factors. If you have low bone density, your doctor will likely recommend a repeat scan in one to two years to see whether your bones are getting weaker or staying stable.

If you have osteoporosis and start treatment, your doctor will usually repeat the scan after two years to check whether the treatment is working. After that, scans may be done every one to two years, or your doctor may space them further apart depending on how well your bones are responding to treatment.

Other tests your doctor might order

Your doctor may order blood tests to check your calcium, vitamin D, and other minerals that affect bone health. A blood test can also help rule out other conditions that weaken bones, such as thyroid disease or kidney problems. These tests do not diagnose osteoporosis, but they help your doctor understand why your bones may be weak and what treatment might help.

A regular X-ray cannot detect osteoporosis until bones are already very weak and may have begun to break. If you have back pain or a suspected fracture, your doctor may order an X-ray to look for breaks, but this is different from a bone density scan.

What happens after diagnosis

If your scan shows low bone density or osteoporosis, your doctor will talk with you about ways to slow bone loss and reduce your fracture risk. This may include changes to diet and exercise, vitamin D and calcium supplements, or medications that strengthen bones. Your doctor will also discuss fall prevention, since avoiding falls is one of the most important ways to prevent broken bones.

You do not need to start treatment immediately after diagnosis. Your doctor will consider your age, your T-score, your other health conditions, and your personal risk of breaking a bone before recommending treatment. Some people with low bone density never develop osteoporosis or break a bone, while others benefit greatly from early treatment.

Preparing for your bone density scan

You do not need to fast before a bone density scan or stop taking any medications. Wear loose, comfortable clothing without metal buttons, zippers, or snaps, since metal can interfere with the scan. Remove jewelry, watches, and belts before the scan begins.

Tell your doctor if you have had a barium X-ray or injected contrast dye within the past two weeks, since these can affect your bone density results. If you are pregnant or think you might be, tell the technician before the scan, since the radiation exposure is not recommended during pregnancy.

Frequently Asked Questions

Is a bone density scan safe?

Yes. The radiation dose from a bone density scan is very small—about one-tenth the radiation from a chest X-ray. The test causes no pain and has no side effects. You can have the scan done as often as your doctor recommends without worry about radiation harm.

Can I be diagnosed with osteoporosis without a bone density scan?

No. A bone density scan is the only test that can diagnose osteoporosis. A doctor cannot diagnose it based on symptoms alone, blood tests, or regular X-rays. If you have broken a bone from a minor fall or injury, your doctor may suspect osteoporosis and order a scan to confirm it.

What if my results show normal bone density?

If your scan is normal, you can focus on keeping your bones strong through exercise, adequate calcium and vitamin D intake, and avoiding smoking and excess alcohol. Your doctor will tell you when to have your next scan, which may be in 10 years or longer depending on your age and risk factors.

Do I need a scan if I have no symptoms?

Yes. Osteoporosis has no symptoms in its early stages, which is why screening scans are important. Many people do not know they have weak bones until they break one. If you are in an age group that should be screened, a scan can catch bone loss before a fracture happens.