How to Read a Bone Density Scan: Understanding T-Score vs. Z-Score

If you are scheduled to have (or have already had) a bone density scan, you may have questions about your scoring results. With terms like T-score, Z-score, DXA and other acronyms, it can get a little confusing. This guide will discuss what to expect at these scans, what the scores mean and address other common questions regarding this scanning technique. Understanding these results can guide you in taking effective actions to improve your bone health.

While this guide outlines potential findings, your doctor will provide your official diagnosis and next steps during your follow-up appointment. For those who prefer early access, PocketHealth offers secure instant access as soon as your report is uploaded. This gives you a chance to review your results and prepare questions for your doctor in advance.

 

 

What does DXA/DEXA stand for?

DXA or DEXA stands for dual-energy X-ray absorptiometry and is the most common and effective method used to measure bone density. A DXA scan uses X-ray beams at 2 different energies to calculate bone density. This scan may also be called a bone mineral density (BMD) test.

 

What is a bone density test?

Your bones are alive, constantly forming and breaking down. While it may seem like bones are purely solid, they are actually composed of an intricate scaffold of bony struts (called trabeculae). In healthy people, bone density peaks in teenage years and decreases as people age. A healthy diet and exercise can help slow this decay.

A bone density scan measures how porous or dense your bones are. Denser calcified bone tissue is usually stronger because it has more bony struts and fewer pockets or holes. Bones with fewer dense calcified struts are weaker and more likely to fracture.

Patients with abnormally low bone density have a condition called osteoporosis, which can increase risks of fractures from low-impact injuries like falls. It is very common; approximately 10 million Americans and 2 million Canadians have osteoporosis. If your doctor has recommended you get a bone density test, you’re not alone: all adults over the age of 65 should have annual bone density testing to determine whether they’re at risk of osteoporosis.

 

Who should have a DEXA test?

Loss of bone density can happen to anyone, but patients assigned female at birth (AFAB) are more prone to getting the disease due to factors like estrogen depletion with age, smaller bone sizes and naturally less dense bones compared to those assigned male at birth (AMAB). Because of this, the recommended screening age is 65 for AFAB patients and 70 for AMAB patients.

Patients may also be recommended to get a bone scan under these circumstances:

• Post-menopausal: When patients are post-menopausal and don’t take estrogen to compensate, they are at higher risk. In the U.S. one in four AFAB patients over 65 get osteoporosis.
• When taking certain medications: There are several medicines that can have the side effect of bone loss, such as anti-seizure medications or corticosteroids.
• Pre-existing conditions: Certain diseases or conditions can increase bone loss, including liver or kidney disease, hyperthyroidism and other thyroid conditions or Type 1 diabetes.
• Family history of osteoporosis: This increases risk of also developing the condition.
• Smoking: Nicotine slows osteoblast production, which are bone-forming cells. This means less bone density.
• Certain body types: Post-menopausal patients who are less than 125 pounds and over 5 feet 7 inches may have increased risks.
• History of fractures: This is particularly pertinent when the trauma that caused these fractures would have been considered mild.
• Lost height: Patients who have lost more than an inch of height within a year or so.
• Abnormally high bone turnover: The process of bone resorption and replacement is called bone turnover. Higher than normal rates of this can suggest bone conditions.

 

What happens during a bone density test?

Before your DEXA scan, your doctor will likely have you stop all calcium supplements one to two days before your appointment, though these times and instructions may vary. When you prepare for your appointment, try to avoid dressing in clothes with metallic components such as zippers and buttons and also avoid wearing piercings or jewelry.

You will be asked to lie on your back on the exam table, fully clothed. The scanner arm will move over your hip and low back while a second scanner arm moves beneath you. Some facilities have a separate scanning device to assess the wrist and hand while others have that included within the main bone density scanning machine.

The technician will need you to hold as still as possible and they may prompt you to hold your breath for brief periods of time. Images will be captured on a screen so they can be saved and sent to a radiologist who specializes in assessing medical imaging to interpret. Typical scan times are ten to thirty minutes. This scan is non-invasive and you should be able to go about your day as usual afterward.

 

Understanding your results

DEXA result turnaround times depend on the radiologist’s and your referring doctor’s schedules. It can sometimes take a week or more, especially if you receive them at your follow-up appointment. With PocketHealth, you can get your results much faster. You’ll have secure access as soon as they’re uploaded, meaning you’ll likely see them before your upcoming appointment. This gives you time to review the findings and prepare for your next medical visit.

Although your doctor will explain your results to you, here is an educational overview of common DEXA result terms and what they may mean.

What’s T-score vs. Z-score?

Your bone density measurement is interpreted by comparing your BMD value (in grams per cubic centimeter) to others of the same sex using 2 statistical tests that use the bell curve: the T-score and Z-score.

Understanding T-score

The T-score range or number on your bone density test report indicates how much your bone density differs from the bone density of an average, healthy 30-year-old. Your T-score number is measured in units of Standard Deviation (SD). The greater the SD, the greater your bone mass deviates from the average.

For example, if your bone density report shows:

• 0 SD T-score: Your bone density is equal to that of an average, healthy 30-year-old, or zero standard deviations away from the average.
• +1 or +2 SD T-score: Your bone density is greater than the average score, indicating you are one or two standard deviations away from average bone density for an average, healthy 30-year-old.
• -1 or -2 SD T-score: Your bone density is less than the average score, indicating you are one or two standard deviations away from average bone density for an average, healthy 30-year-old.

T-scores can also help your doctor determine whether you have osteopenia or osteoporosis, serious conditions that can lead to increased fracture risk. For example:

• A T-score of -1 to -2.5 SD: Indicates osteopenia, which is defined as low bone density compared to the average population.
• A T-score of -2.5 SD or more: Indicates osteoporosis, which means you have lower bone mass than approximately 95% of healthy 30-year-olds of your biological sex.

Understanding Z-score

The Z-score range or number on your results compares your bone density to the average bone density of people your own age and sex and uses the same units of measurement (SD) as the T-score. For example, a -1 or -2 SD Z-score indicates that your bones are less dense than what’s average for your age and sex.

Z-scores are only used to analyze the bone density of children, young adults, pre-menopausal women and men under 50 years of age. Z-scores, along with analysis of lifestyle factors, can also help indicate secondary osteoporosis, a type of osteoporosis caused by certain illnesses, medications or lifestyle factors.

While the T-scores and Z-scores of one bone density test cannot show whether you are losing bone mass, they do compare you to an average. Your doctor may recommend blood tests to track markers of bone density loss over time.

What does FRAX mean?

One primary concern with osteopenia or osteoporosis is an increased risk of fractures. The Fracture Risk Assessment Tool (FRAX) from the World Health Organization calculates your risk of suffering a ‘fragility fracture’ (i.e. fracture due to a fall from standing) in the next decade by analyzing various risk factors, including bone density.

FRAX also takes into consideration the following factors:

• Age
• Sex
• BMI (Body Mass Index measured using weight-to-height ratio)
• BMD in the hip
• Fracture history
• Secondary osteoporosis
• Medication use, particularly steroids
• Parental hip fracture
• Rheumatoid arthritis
• Current cigarette smoking
• Alcohol intake

After analysis, the doctor can determine the FRAX percentage, which indicates the likelihood of developing a fracture in the hip, arm or spine within the next ten years. This is mainly used to determine what medication may be most helpful.

• 10% or less FRAX score: A normal FRAX score indicating the risk of fragility fracture in the next ten years is less than 10%.
• 10% to 20% FRAX score: A moderate FRAX score indicating the risk of major fragility in the next ten years is between 10% and 20%.
• 20% or higher FRAX score: A high FRAX score strongly suggests the risk of fragility fracture in the next 10 years is 20% or higher.

 

Understanding your treatment options

If you do receive an osteoporosis diagnosis, there are several treatment options available, such as:

• Medication: There are multiple medications available, which can help slow bone loss or promote bone growth. For example, bisphosphonates are most commonly prescribed and can be taken orally or via IV infusion. Hormone treatments, like estrogen, may also be an option.Talk to your doctor about the best choices for you.
• Lifestyle changes: Frequent weight-bearing exercises are important to help strengthen bones while improving balance and strength. This is key to preventing falls (i.e., the more active and fit you are, the lower your chances of falling and breaking a bone).
• Diet changes and supplements: Calcium is the main mineral found in bones, therefore, a balanced diet needs calcium to maintain strong, healthy bones. Getting the required amount of calcium from diet alone can be difficult, so you’ll likely take calcium supplements, as well as additional vitamin D, which helps your body better absorb calcium.

Exercise considerations for patients with osteoporosis

As mentioned, exercise is a very important component of bone health, both for building bone strength and improving balance to avoid falls. That said, if you have been diagnosed with low bone density, there are two factors to keep in mind when undertaking an exercise regimen:

• When working on balance, take extra precautions: The point of working on balance is to reduce your fall risk. The last thing you want is to fall while practicing your balance. If you feel particularly unstable, you may want to ask your doctor for advice on how to safely incorporate low-risk balance routines. Having something to hold onto and practicing on soft surfaces are some examples of precautions.
• Avoid certain movements: For patients with advanced bone loss, certain movements can actually increase the risk of or even cause fractures. Examples include bending forward at the waist (as if to touch your toes), movements that twist your torso (like golfing), high-impact exercises (like jogging) and exercises that strain your low back. It may be beneficial to consult your doctor or a physical therapist to get a list of movements to avoid. If you use a personal or fitness trainer, be sure to let them know of these restrictions too. They can help you replace these movements with safer exercises.

 

Frequently asked questions

Here is a quick overview of commonly asked questions regarding bone density scan results.

Does a bone density test show cancer?

Bone density tests are primarily used to determine fracture risks and osteoporosis. However, abnormalities found in the scan can indicate cancerous lesions or the spread of cancer to your bones. This is not an actual cancer diagnosis, however, and the abnormalities may be due to a completely benign cause, so try not to panic. Additional testing will likely be recommended before any kind of diagnosis or conclusions.

What happens if bone density is low?

Low bone density can mean an increased risk for bone fractures. If the bone density is low enough, it is classified as osteoporosis, which is when bones are so weak and brittle that very mild trauma can cause fractures and injuries. Fortunately, there are treatments to reduce this risk.

Does arthritis show up on a bone density test?

While DEXA scans can show signs of bone loss, which can be linked to certain types of arthritis, they cannot actually diagnose arthritis. Other imaging types, such as ultrasounds and MRIs, are more commonly used to reach this conclusion.

 

How PocketHealth can help you understand your bone density scan

Waiting for your follow-up appointment to discuss your bone density results can be nerve-wracking, but you can easily access your images and results with PocketHealth as soon as they are uploaded. You can also store and share your results directly from your device.

If you encounter some complex medical terminology in your bone density scan report, PocketHealth Report Reader can help. Report Reader provides definitions for the medical terms in your report, making it easier to comprehend your results and spotlights any follow-up recommendations so you can feel informed and confident when speaking to your doctor at your next appointment.

“With Report Reader, I get explanations for words [in my report] that I don’t understand. I can now discuss my health with my family doctor with more confidence and have a better understanding of what is going on.”

– PocketHealth Patient

 

Stay on top of your bone health—and your bone density results

Now you have a general overview of the different scoring types, BMD, lifestyle and other treatments and how to determine your personal fracture risk. You’ve gained a lot of important information by reading this article, but you can learn more by accessing your bone density report through PocketHealth and tracking any progressions over time.

Depending on your results, you may be taking treatment options into consideration to discuss with your doctor. MyCare Navigator is especially helpful for offering personalized insights and identifying any recommended follow-up steps within your report. It helps you formulate relevant questions to ask your doctor so you can make the most of your consultation, enabling you to become a more informed participant in your health journey.

For Blair, celiac disease resulted in early bone density loss. At just 32, her bone density resembled that of a 60-year-old woman. However, by changing her lifestyle, she has seen improvements in her health, and by keeping track of her bone imaging records, she stays on top of her condition.

 

Medical content review provided by Ben Fine, MD. Any health-related information contained in this post is intended to provide general education only and is not medical advice. This should not be used as a substitute for the advice you receive from your healthcare provider.