Osteoporosis is a bone disease that develops because of bone loss. The result is weak and brittle bones that are prone to fractures even from low-impact movements. To find out if you have or are at risk for osteoporosis, you will need a bone density test.
A bone density scan produces a number called a T-score. The numerical value will give your doctor an idea of where your bone density currently is. It can tell them if you already have osteoporosis or if you are at risk for developing it.
T-scores between -1 and -2.5 indicate that a person has low bone mass, but it’s not quite low enough for them to be diagnosed with osteoporosis. A diagnosis of osteoporosis is made if a person’s T-score is -2.5 or lower.
The lower a person’s T-score, the more severe their bone loss is, and the more at risk for fractures they are.
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What Does T-Score Measure?
Bones have microscopic holes throughout them, and their structure is often compared to a honeycomb. When bone loss occurs, the holes in the bones get bigger. Bigger holes lead to weak and brittle bones. T-score tests are used to help determine how big the holes in the bone are.
A person’s T-score test may indicate that some bone loss has occurred, but not enough for an osteoporosis diagnosis to be made. If the holes in the bones are bigger than normal—but not yet big enough to be considered osteoporosis—a person might be diagnosed with a less severe version of osteoporosis referred to as osteopenia.
Osteopenia is also often diagnosed using a bone density test, which measures both bone mass and bone strength. While bone mass is the amount of bone tissue found in the skeleton, bone density is the amount of mineral content in bone tissue.
T-scores measure the number of minerals in a person’s bone. A person’s level of bone loss is compared to that of a typical, healthy 30-year-old adult. The comparison helps determine a person’s bone density.
How Osteoporosis Is Diagnosed
Bone Density by Age
Losing bone density is part of the normal aging process. As you age, your bone density will change—however, that does not necessarily mean that you will develop osteoporosis. Other factors, such as diet and exercise, also play a role in the onset of osteoporosis.
The process of bone remodeling is a cyclical event that occurs throughout your life. It involves cells (osteoclasts) breaking down old bone tissue to allow the cells that rebuild new bone tissue (called osteoblasts) to replace the lost bone.
Up to the age of 25, more new bone is being made than osteoclasts can take away, which leads to an increase in bone density. From the age of 25 to age 50, the process is stable and bones are being broken down and built back up in equal amounts.
When a person reaches age 50, the breakdown process accelerates and outpaces the body’s ability to reform new bone. This leads to progressive bone loss.
Everything to Know About Bone Health As You Age
T-Score vs. Z-Score
Although T-scores are typically the first choice for doctors looking to gauge the level of bone loss, a Z-score can also be beneficial to help diagnose osteoporosis or the amount of bone loss in women, children, and young men.
The T-score will compare a patient’s bone density against that of a healthy 30-year-old person, while the Z-score compares the results to someone in the same age and sex group as the patient.
For example, a 40-year-old woman getting a test for her bone mineral density will have a Z-score based on the average bone density among 40-year-old women.
T-scores are used to determine primary osteoporosis, which exists on its own without any other cause. The test is used most often for people over the age of 50 who experience accelerated bone loss and for people who have already had a fracture caused by osteoporosis.
Z-scores are designed to identify if there is a secondary cause of bone loss. They are often used for younger adults, children, or premenopausal women.
Is a T-Score Better Than a Z-Score?
T-scores and Z-scores have their own strengths. For example, T-scores are better at determining if you have osteoporosis, while Z-scores are better at assessing your 10-year risk for developing osteoporosis or experiencing fractures.
You can think of a Z-score as a preventive screening to help you better understand your bone health.
The Stages of Osteoporosis
Who’s At Risk?
Women and people over the age of 50 are the most at risk for osteoporosis. However, anyone can develop the condition.
There are certain other populations that are at a higher risk. One study looked at the total number of osteoporosis cases in the United States and found that the group with the most total cases were men and women of non-Hispanic White descent.
Who Needs a Bone Density Test?
The Bone Health & Osteoporosis Foundation suggests that you get a bone density test if you:
- Break a bone after the age of 50
- Have lost a half of an inch of height or more within one year
- Have back pain that might be caused by a spine break
- Have had an X-ray that shows bone loss in your spine
- Are a female aged 65 or older
- Are a male aged 70 or older
What Causes Osteoporosis?
Getting a Referral
To get a bone density test, you will first have to go to your primary care provider. They can assess your risk or refer you to a specialist who can. The provider or specialist can book the test if it is appropriate for you.
Your insurance provider might be able to tell you where the test is available. Tests can often be done in radiology departments in hospitals and private radiology clinics. In some cases, medical practices are equipped for this type of test.
Bone Density Tests
Several tests can be used to determine a T-score.
DEXA Scan
A dual-energy X-ray absorptiometry test (DEXA scan) is typically the first type of test a person gets to check their bone density. It works by using two separate types of low-dose X-rays, both of which are sent into the bones and soft tissues. However, each ray is absorbed differently.
The two separate absorptions allow doctors to get a better picture of the structure of the bone. The hip and spine are typically examined during a DEXA scan because a fracture in these areas can lead to more severe consequences than breaks in other parts of the body.
The bone scan is painless and lasts roughly 15 minutes. You do not need to undress, but zippers or buttons should be out of the way in the area that’s being scanned because they can interfere with the results.
The DEXA scan relies on T-scores to determine the level of bone density that a person has. If the results indicate that you have or are at risk of having osteoporosis, you may have to repeat the test once every one to two years.
After a diagnosis of osteoporosis is confirmed and a treatment plan is developed, you will likely have a follow-up test in about a year.
What Are Bone Scans Used For?
FRAX Calculator
The fracture risk assessment tool (FRAX) was developed by the World Health Organization to help doctors assess a person’s fracture risk. The scan examines bone density in the part of the hip where the thigh bone reaches the ball that sits in the hip socket (the femoral neck). The calculator uses the results to determine the probability that someone will experience a fracture in the next 10 years.
The calculator was designed as a preventative screening to make sure that people with low bone density can address the concern before it becomes osteoporosis or leads to fractures. The test can also be used to determine the risk of fractures in people who already have osteoporosis, which can help their doctors develop a treatment plan.
There are certain limitations to the T-score assessment, therefore the FRAX calculator can be used to help bridge the diagnostic gaps and determine someone’s fracture risk.
Peripheral Tests
Peripheral tests or screening tests are typically done to measure the bone density in the lower arms, fingers, hands, or wrists. These tests include:
- Peripheral dual-energy X-ray absorptiometry (pDXA)
- Quantitative ultrasound (QUS)
- Peripheral quantitative computed tomography (pQCT)
These tests are designed to determine if a person needs a DEXA scan based on the bone density in other parts of their body.
Which Test Comes First?
Depending on the type of fracture that you experienced, your age, and other risk factors, a DEXA scan is typically the first-line diagnostic option for osteoporosis.
Peripheral tests and the FRAX calculator cannot be used to diagnose osteoporosis; rather, they are additional tools to help diagnose bone loss and prevent fractures.
Osteoporosis T-Score Chart
The T-scores used to determine osteoporosis are divided into three categories: low risk, medium risk, and high risk.
| Percentile | T-Score | Example | Your Risk: Explained |
| Low Risk | -1.0 or above | -1.0, 0, +0.5 | This is within the normal bone density range. People in this category are at low risk of osteoporosis. |
| Medium Risk | -1.0 to -2.5 | -1.1, -1.5, -2.4 | This score is considered low bone density. People in this range are at medium risk for fracture or osteoporosis. |
| High Risk | -2.5 or below | -2.5, -3.0, -4.0 | Anything below -2.5 indicates osteoporosis and a high risk for fractures. People with these scores have osteoporosis that ranges in severity. |
Interpreting T-Score Results
Once you have your T-score, you can talk to your doctor about your results and what they mean for the future health of your bones.
Low Risk
When you are at low risk for fractures or osteoporosis, you do not need any treatment. Your bone density is considered normal.
If you are at this stage, you could opt to keep a watchful eye on your calcium and vitamin D intake, because these nutrients are vital to healthy bones. You may also want to implement an exercise program that could help keep your bone density as high as possible as you get older.
Medium Risk
Not everyone in this category will develop osteoporosis, however people with a medium risk are more likely than those that fall into the low-risk category.
As low bone density is a risk factor for osteoporosis, you may want to take steps to slow bone loss, such as making sure that you are getting the daily recommended amount of vitamin D and calcium in your diet and getting regular exercise such as walking, dancing, or jogging.
Depending on where on the scale of medium risk you fall, your doctor might prescribe a medication that can help to prevent further bone loss and therefore prevent osteoporosis.
Medications to Prevent or Reverse Bone Loss
High Risk
People in the high-risk category are diagnosed with osteoporosis. Your doctor will prescribe medications to slow bone loss or to help rebuild new bone tissue.
Lifestyle changes that promote bone health can also be helpful in slowing the progression of the disease. However, talk to your doctor before starting an exercise program to make sure that you do not undertake physical activity that puts you at risk for breaking a bone.
What Is Secondary Osteoporosis?
Improving Your Bone Health
Your T-score gives you the information that you need to strengthen bone density in a meaningful way. Once you know your T-score, you can take steps to help prevent osteoporosis from developing or to prevent more bone loss.
Some specific areas where you can make changes to improve your bone health include:
- Diet: Calcium and vitamin D are crucial for bone health and can help to slow bone loss. It’s important that you get enough of these key nutrients in your diet. However, if you cannot get enough from dietary sources, taking calcium and vitamin D supplements is an option.
- Exercise: Being sedentary can reduce the body’s ability to rebuild new bone tissue. Exercising safely, aiming to get about 150 minutes per week, can be beneficial for bone health.
- Medications: If you have osteoporosis, your doctor will prescribe you medications to either prevent further bone loss or rebuild new bone tissue.
Menopause, Osteoporosis, and Hormone Therapy
Summary
When your bone density is tested, your healthcare provider will get a numerical score that tells them if you already have osteoporosis or are at risk for developing it. One of the numbers is called a T-score, which tells whether your bone density is low enough to be considered osteoporosis.
If your T-score is not yet in the osteoporosis range, there are some steps you can take to prevent it from getting there, such as getting more calcium in your diet and exercising.
Complications of Osteoporosis and Related Conditions
Frequently Asked Questions
Is a T-score always accurate?
No bone density test is 100% accurate. However, T-scores are the most accurate measurement used to determine osteoporosis risk and loss of bone density.
Can I improve my T-score?
In some cases, a T-score can be improved. However, it depends on where your score falls within the risk range and your lifestyle. Building up your bone density may involve taking medications as prescribed, eating plenty of foods that contain calcium and vitamin D, and exercising regularly.
When should I have a bone density screening?
People who are going through menopause, are over the age of 50, or have recently experienced a fracture from a low- or medium-impact activity may need to have a bone density screening. People who smoke and those who drink alcohol in excess are also at a higher risk for early bone loss and could benefit from a bone density screening. If you are not sure where you fall on the risk scale, ask your doctor.
Learn MorePostmenopausal Osteoporosis
9 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Angelica Bottaro
Bottaro has a Bachelor of Science in Psychology and an Advanced Diploma in Journalism. She is based in Canada.
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