Bone density screenings are used to diagnose or determine your risk of osteoporosis or of later fracturing a bone. If you’re already undergoing treatment for osteoporosis, they may be used to check whether treatment is working.

The most common type of bone density test is called a dual-energy X-ray absorptiometry (DEXA or DXA) scan.

A DEXA scan will return two different scores — a t-score and a z-score — which give you information about the density of your bones. Let’s take a closer look at these scores, how the DEXA scan works, and when you might need one.

A note on sex and gender

You’ll notice that “women” is used to share stats and other data points on people assigned female at birth.

Although we typically avoid language like this, specificity is key when reporting on research participants and clinical findings.

The studies and surveys referenced in this article didn’t report data on, or include, participants who were transgender, nonbinary, gender nonconforming, genderqueer, agender, or genderless.

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Both the t-score and the z-score are comparisons of your bone density with the average bone densities of different populations. Let’s look at each one individually.

What’s a t-score?

A t-score reflects your bone mineral density (BMD) compared with the average BMD of a young, healthy adult of the same sex.

What’s a z-score?

A z-score compares your BMD with the average BMD in your own age group, taking both sex and body mass index (BMI) into account.

Both t-scores and z-scores represent your bone loss as a standard deviation compared with either young adults or peers.

In other words, a score of 0 means you have average bone density relative to the group you’re being compared against. A negative score represents your level of bone loss, while a positive score would mean you have greater than average bone density.

T-score results

T-score rangeDescription
1 and abovenormal bone density
Between 1 and 2.5osteopenia (below normal BMD)
2.5 and lowerosteoporosis (low BMD)

T-scores compare your BMD with that of healthy adults at the normal peak of physical development, which makes it useful for diagnosing osteopenia and osteoporosis.

Z-score results

Z-score rangeDescription
-1.5 and abovetypical bone density for peer group
Lower than -1.5atypical BMD, needs investigation

Z-scores are a comparison of your BMD and that of your peer group. Because bone density naturally decreases with age, it’s possible to have a z-score close to zero but still have low BMD.

This score is more useful for diagnosing secondary osteoporosis, especially for children and younger adults.

If you have a high z-score, you may be referred to an endocrinologist to look at secondary causes of osteoporosis, which may include:

  • gastrointestinal diseases
  • autoimmune conditions
  • kidney conditions
  • medications

The DEXA scan is the most common type of bone density screening. It’s a painless outpatient procedure that’s similar to other common X-ray exams.

If you’re having a central DEXA scan, the technician will have you lie on a padded table. They might brace your legs with a cushioned box. A scanner will pass over your hips and lower spine, and you’ll need to stay very still.

Sometimes you might have a peripheral DEXA scan, which uses a smaller scanner to check the bone density of your heel, forearm, wrist, or finger. This may be more useful if you’ve had hip replacement or spinal surgeries.

Experts consider the central DEXA scan to be more reliable for diagnosing osteoporosis and determining your risk of bone fracture.

Often, older adults with spine osteoarthritis have bone spurs that can be calculated into the bone density interpretation and falsely elevate the numbers. The hip may provide a more accurate read in someone who has osteoarthritis of the spine.

If you’ve received a diagnosis of osteopenia or osteoporosis, it’s important to follow your treatment plan. Often this will include:

There aren’t any randomized studies to show whether follow-up bone density scans affect your outcome. It’s not uncommon to repeat the test in 1 to 2 years to help determine whether your treatment plan needs to be revised.

Most hospitals and some private practices have a radiology department that can perform a DEXA scan.

In order to have the procedure, you’ll likely need a referral from a primary care physician or other specialist. The scan will usually be handled by a technician and reviewed by a radiologist, and then the results will be sent back to the referring doctor.

If you’d like to have a DEXA scan, the best starting place is consulting with a primary care doctor or a gynecologist. They’ll be able to either write you a referral or recommend a specialist.

While DEXA scans are the most common tool for diagnosing osteoporosis, there are other tests that can measure BMD.

Quantitative computed tomography (QCT)

This type of CT scan may be more useful if a doctor believes your spine is an area of concern. However, it generally exposes you to more radiation than a DEXA scan, and the availability is more limited.

Biomechanical computed tomography (BCT)

This method uses special software to calculate your bone strength based on CT scans you may have already completed.

Radiofrequency echographic multispectrometry (REMS)

REMS uses a type of ultrasound to quickly estimate your BMD without exposing you to any radiation. This is a newer technology that might not be available everywhere yet.

Magnetic resonance imaging (MRI)

MRI scans have been proposed as a method of measuring bone density. The equipment is widely available, and the scans don’t expose you to any ionizing radiation, but this method still needs more research.

You may still have some questions about bone density scores. Let’s answer some of the most common questions.

Which is more accurate, a t-score or a z-score?

Both scores are considered accurate, but they’re used for different purposes. T-scores can be used to diagnose osteopenia and osteoporosis, while z-scores can help diagnose secondary osteoporosis.

Can I improve my t-score or z-score?

It’s possible to increase your BMD — and improve your scores — with appropriate diet and targeted exercise. However, exercise and supplements are usually not enough to reduce the risk of fractures for someone who has received a diagnosis of osteoporosis. Talk with a doctor to find out how you might safely increase your bone density.

Who should get a bone density screening?

The U.S. Preventive Services Task Force (USPSTF) — a nongovernmental advisory board — recommends bone density scans for women over the age of 65 and for women who postmenopausal and under the age of 65 who may have an increased risk of osteoporosis.

There are two common scores for bone density: a t-score and a z-score. These scores are obtained by getting a DEXA scan.

T-scores compare your bone density with that of a young adult, while z-scores compare your bone density with that of your peer group. They can be used to diagnose osteopenia, osteoporosis, or secondary osteoporosis or to estimate your risk of future bone fracture. They might also help determine if your treatment plan is effective.

If you think you might need a bone density scan, speak with a doctor about your options.