Osteoporosis is diagnosed with a bone density scan, not blood work or X-rays

The standard test for osteoporosis is called a DEXA scan (dual-energy X-ray absorptiometry). It measures how much mineral is packed into your bones — your bone density — and compares it to the bones of a healthy young adult. The scan takes about 10 to 30 minutes, involves no needles, and uses a very small amount of radiation, far less than a chest X-ray.

A regular X-ray can show a fracture, but it cannot detect osteoporosis until the bone loss is severe. Blood tests alone cannot diagnose osteoporosis either, though your doctor may order them to rule out other causes of bone loss, such as thyroid problems or vitamin D deficiency. The DEXA scan is the only test that can catch osteoporosis early, before a fracture happens.

Key Takeaways

  • A DEXA scan is a quick, painless X-ray that measures bone density and is the standard way to diagnose osteoporosis.
  • Your doctor will compare your bone density to a healthy young adult's and give you a T-score, which determines whether you have normal bones, low bone mass, or osteoporosis.
  • The scan usually focuses on your hip and spine, the places most likely to fracture if your bones are weak.
  • Medicare covers a DEXA scan once every two years for women over 65 and men over 70, and more often if you have risk factors.
  • You do not need to fast, stop medications, or prepare in any special way before the test.

What happens during a DEXA scan

You lie on a padded table fully clothed while a scanning arm passes over your body. The machine sends two X-ray beams through your bones and measures how much energy each beam absorbs. Denser bones absorb more energy. The whole process is quiet and still — you do not feel anything.

The scan usually covers your lower spine and hip, since those are the sites where fractures cause the most disability in older adults. Some doctors also scan the forearm. If you have had recent spine surgery or cannot lie flat, your doctor may adjust the scan or use a different method.

Understanding your T-score

After the scan, your doctor will give you a report with a T-score. This number compares your bone density to that of a healthy 30-year-old. The T-score tells you whether your bones are normal, whether you have low bone mass (sometimes called osteopenia), or whether you have osteoporosis.

A T-score of −1.0 or higher means your bones are normal. A T-score between −1.0 and −2.5 means you have low bone mass. A T-score of −2.5 or lower means you have osteoporosis. If your score is between −1.0 and −2.5, your doctor may recommend steps to slow bone loss, such as more calcium and vitamin D, weight-bearing exercise, and sometimes medication.

Your doctor may also calculate a 10-year fracture risk using a tool called FRAX. This tool combines your T-score with your age, weight, and medical history to estimate your chance of breaking a hip or spine bone in the next 10 years. This helps your doctor decide whether medication is right for you.

Who should be tested and when

The U.S. Preventive Services Task Force recommends that all women age 65 and older have a DEXA scan. Men age 70 and older should also be tested. Younger people — both men and women — should be tested if they have risk factors for bone loss, such as a family history of osteoporosis, long-term use of corticosteroids, rheumatoid arthritis, or a previous fracture from a minor fall.

If your first scan is normal, your doctor will tell you when to have the next one. For most people with normal bone density, a repeat scan every 10 years is reasonable. If you have low bone mass or osteoporosis, or if you are taking bone-strengthening medication, you may need a scan every one to two years to see whether treatment is working.

What to do before your scan

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

If you have had a CT scan or nuclear medicine scan with contrast dye in the past week, tell your doctor before your DEXA scan, because the dye can affect the results. If you are pregnant or think you might be, tell the technician — DEXA scans are not done during pregnancy because of radiation exposure, even though the dose is very small.

What happens if the scan shows osteoporosis

A diagnosis of osteoporosis does not mean a fracture is inevitable. It means your bones are weaker than normal and your risk of breaking a bone is higher. Your doctor will talk with you about ways to slow bone loss and reduce fracture risk. These may include calcium and vitamin D supplements, weight-bearing and muscle-strengthening exercise, fall prevention, and sometimes medication.

Your doctor may also order blood tests to check your vitamin D level, kidney function, and thyroid, since these affect bone health. If you have had a recent fracture, your doctor may want to know more about how it happened and whether you fell from standing height or from a minor bump — this helps determine how aggressively to treat.

Other bone density tests

DEXA is the most common and most widely covered test, but other methods exist. Quantitative ultrasound uses sound waves instead of X-rays and can be done at the heel or shinbone. It is faster and involves no radiation, but it is less precise than DEXA and is not used to diagnose osteoporosis on its own — it is mainly used to screen for risk.

CT scans can measure bone density in the spine and are sometimes used if you have had spine surgery or cannot lie flat for a DEXA scan. Peripheral DEXA scans the forearm or heel and is portable, but it is less reliable than a full DEXA scan of the hip and spine.

Frequently Asked Questions

Is a DEXA scan safe?

Yes. The radiation dose from a DEXA scan is very small — about one-tenth the dose of a chest X-ray. You are not radioactive after the scan, and there are no side effects. The only reason to avoid it is if you are pregnant.

How much does a DEXA scan cost?

Cost varies by location and whether you have insurance. Medicare covers a DEXA scan once every two years for women over 65 and men over 70 at no cost to you if you meet coverage rules. Private insurance coverage also varies. Ask your doctor's office or the imaging center for a price estimate before your appointment.

Can osteoporosis be diagnosed from a regular X-ray?

No. A regular X-ray shows bone loss only when it is severe — usually 30 percent or more. By that point, fracture risk is already high. A DEXA scan can detect bone loss much earlier, when there is still time to slow it down with treatment.

What if my DEXA results are normal but I still break a bone easily?

Bone density is only one part of bone health. Some people with normal DEXA scores still fracture easily because of poor bone quality, balance problems, or medications that affect bone. Talk to your doctor about your fracture history and other risk factors. They may recommend additional testing or a different approach to prevention.

How often do I need a repeat DEXA scan?

If your bones are normal, a repeat scan every 10 years is usually sufficient. If you have low bone mass, a scan every one to two years helps track whether your bones are stable or continuing to lose density. If you are taking osteoporosis medication, your doctor will decide on repeat timing based on your response to treatment.