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

Your guide to understanding T-score vs. Z-score and other common terminology in your bone density scan.

Bone density refers to the structure and mass of your bones. A bone density scan is used to determine how porous or dense your bones on a scale. This scan may also be called a bone mineral density (BMD) test or a dual-energy x-ray absorptiometry (DXA) scan. Denser bone tissue is stronger because it has very few pockets or holes in it. Porous bone tissue contains pockets or holes that weaken the overall structure of the bone, making it more likely to fracture.

How porous your bones are is a key indicator of how likely you are to develop osteoporosis, even if you show no other signs of the disease. Approximately, 10 million Americans and 2 million Canadians have osteoporosis. If your doctor has recommended you get a DXA scan or 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.

A bone density scan is an important diagnostic tool that both you and your doctor can access. Under the Health Insurance Portability and Accountability Act of 1996 (HIPAA) in the U.S. and the national Privacy Act in Canada, having access to your medical records is required by law.

Being able to review the radiologist’s report for your bone density scan lets you have more informed discussions with your healthcare provider about your results, but understanding the terminology in your report is key. This article clarifies the common terms you will come across when reviewing your bone density scan report, so you can have a complete understanding of your results before your follow-up appointment.

What does DXA stand for?

DXA stands for dual-energy absorptiometry and is the most common and effective method used to measure bone density. A DXA scan uses two types of X-ray beams to measure bone density by analyzing both mineral and soft tissue density.

What’s T-score vs. Z-score?

A radiologist will analyze your bone density test results by considering 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, sometimes called your DXA score, is measured in units of Standard Deviation (SD). Each unit of SD is equal to an approximate 10% difference in bone mass and shows how far 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. In this case, your bones would have 10% to 20% greater density than the 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. In this case, your bones would have 10% to 20% less bone density than the 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.

• A T-score of -1 to -2.5 SD indicates osteopenia, which is defined as low bone density compared to the average population, but does not indicate pre-osteoporosis.
• A T-score of -2.5 SD or more indicates osteoporosis, which is a bone disease that weakens the structure of the bones, making them more prone to fracture or break.

Understanding Z-score

The Z-score range or number on your bone density test 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 10% to 20% less dense than what’s average for your age and sex.

Z-scores are always 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’s BMC vs. BMD?

Bone mineral density (BMD) and bone mineral content (BMC) help determine osteoporosis risk, but each term means something slightly different.

• Bone mineral content (BMC) uses weight in grams to measure the bone-strengthening minerals found in a specific area of the body. BMC can be measured in any area of the body or throughout the whole body and helps determine bone mineral density (BMD).
• Bone mineral density (BMD) indicates the amount of strengthening bone minerals, such as calcium and phosphorus, in the bones of the area tested. A higher BDM number indicates stronger bones.

What does FRAX mean?

One primary concern for those with osteopenia or osteoporosis is an increased risk of fractures. The Fracture Risk Assessment Tool (FRAX) calculates your risk of getting a fracture in the next decade by analyzing various risk factors, including bone density.

Your doctor will use FRAX to determine your risk of fracture by considering the following:

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

After analysis, your doctor will determine your FRAX percentage, which indicates the likelihood you will develop a fracture in either your hip, arm or spine within the next ten years.

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

How PocketHealth can help you understand your bone density scan

Waiting for our follow-up appointment to discuss the results from your bone density test can be nerve-wracking, but you can easily access your images and results with PocketHealth, often before your follow-up appointment. With PocketHealth you can quickly access your results as soon as the radiologist has completed their report, and 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. Access your records here.

“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

The importance of accessing your bone density results

If your doctor has recommended you get a bone density scan, you may have questions about your results, including the differences between T-scores and Z-scores, BMC and BMD 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 test images and results through PocketHealth.

Reviewing your bone density scan report before your follow-up appointment can help you prepare questions and engage confidently with your physician when discussing the results. Once you understand the terminology and results outlined in your report, you’ll become a more informed participant in your healthcare journey.

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