Bone Mineral Density Tests: What the Numbers Mean

What is a bone mineral density test?

A bone mineral density (BMD) test measures calcium and other minerals in bone. Bones containing more minerals are denser, so they tend to be stronger and less likely to break.

Bones can become less dense as we age or if we develop certain medical conditions. When too much bone is lost, osteoporosis can develop. Osteoporosis causes bones to become weak and brittle, which increases the risk of fractures (broken bones).

Bone mineral density testing can:

• Identify and diagnose osteoporosis.
• Measure the risk of fractures (broken bones).
• Monitor the effectiveness of osteoporosis treatment.

What tests are used to measure bone mineral density?

The most common bone mineral density test is a central dual energy x-ray absorptiometry (DXA or DEXA). DXA uses radiation to measure how much calcium and other minerals are in a specific area of your bone. Because the weak bones that tend to break most often are the hip and spine, DXA usually measures bone mineral density in these bones.

Other tests can also measure bone mineral density or bone loss:

• Quantitative ultrasound (QUS) of the heel: Shows pictures of your bone and can predict your risk of broken bones and osteoporosis. But it is not used to monitor response to osteoporosis treatment, and it does not measure bone mineral density or give as much information as DXA. If the QUS shows that you have a higher risk of osteoporosis or broken bones, your doctor may recommend a central DXA test to confirm the finding.
• Peripheral DXA: Measures bone mineral density, usually in the wrist and heel, using a portable device. This test does not give as much information as central DXA, so it is less accurate. Results showing a higher risk of broken bones or osteoporosis may need to be confirmed with a central DXA test.

What is a T-score?

If you are a woman in postmenopause or a man who is age 50 or older, your bone mineral density test result will be a T-score.

A T-score is the difference between your bone mineral density and 0, which is the bone mineral density of a healthy young adult.

The lower your T-score, the higher your risk of bone fracture.

What is a Z-score?

If you are a premenopausal woman or a man younger than age 50, your bone mineral density test result will be a Z-score. Z-scores are also used for children.

The Z-score is the difference between your bone mineral density and the average bone mineral density for healthy people of your age, ethnicity, and sex.

Who should get a bone mineral density test?

The U.S. Preventive Services Task Force recommends that women over age 65 have a bone mineral density test. The Task Force also recommends this screening for women of any age who have factors, identified by a health care provider who uses a formal risk-assessment tool, that raise their chance of osteoporosis.

More research is needed before the U.S. Preventive Services Task Force can make a recommendation regarding osteoporosis screening in men or how often premenopausal women and women with risk factors should be screened.

What other tools can measure risk of fractures?

Bone mineral density measurement tests are not the only tools that doctors use to predict your risk of fractures.

Doctors may use the Fracture Risk Assessment Tool (FRAX) to estimate risk for fracture. This score uses your age, sex, medical history, country, and other factors. This information, along with your bone mineral density test results, can help health care providers understand your risk for fracture and can guide treatment. For people with osteoporosis or osteopenia, the FRAX score can predict the chances of a major fracture in the next 10 years. The FRAX score can also screen women in postmenopause younger than age 65 for osteoporosis risk.

Read more about osteoporosis and risk factors.

What steps should I take after my test?

It is important that you review your BMD test results with your doctor for a full explanation of what they mean for you. Any diagnoses or treatment recommendations would be based on your BMD test results, age, and other fracture risk factors that you may have. In some cases, your doctor may refer you to a specialist.

Understanding Bone Density Results – Your T-score & Z-score Explained

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Your T-score and Z-score Explained

The T-score

1. The T-score on your bone density report shows how much your bone mass differs from the bone mass of an average healthy 30 year old adult. A bone density test is like any other medical test or measurement. The results for the entire population will be distributed around an average score (the mean).

A T-score is a standard deviation — a mathematical term that calculates how much a result varies from the average or mean. The score that you receive from your bone density (BMD or DXA) test is measured as a standard deviation from the mean. The manufacturers of the DXA machines have programmed them to use a formula to compute these values.

One standard deviation is equal to a 10–12% difference in bone mass. If you are exactly equal to the peak bone mass of an average 30-year-old, you do not deviate at all from the average so your T-score would be 0 standard deviations (SD). If your bones are stronger than the average adult, your bone mass may be +1 or +2 SD indicating that your bones have a mass 10–20% above that of the average 30 year old. If your bones are less dense than the average adult, your standard deviation may be -2 or -3 indicating that your bone mass is 20–30% below that of the average 30 year old.

Definition of Osteoporosis and Osteopenia (low bone density)

Osteoporosis was defined by the World Health Organization in 1994 as a T-score that is 25% lower than the average 30 year old or 2½ standard deviations below the mean or a T-score lower than -2.5.

Some people have low bone density. You may hear this called osteopenia. Osteopenia is defined by the World Health Organization (WHO) as 10% to 25% below an average healthy 30 year old adult, or a T-score between –1. 0 and –2.5 standard deviations below normal. Having a T-score between -1.0 and -2.5 is not “pre-osteoporosis” or a medical condition, but it is very important for people with low bone density to develop a good plan to prevent bone loss and osteoporosis.

The Z-score

A Z-score compares your bone density to the average bone density of people your own age and gender. For example, if you are a 60-year-old female, a Z-score compares your bone density to the average bone density of 60-year-old females.

NOTE: Any post menopausal woman should always request her T-score rather than just her Z-score

A Z-score is helpful in diagnosing secondary osteoporosis and is always used for children, young adults, women who are pre-menopausal, and men under age 50. If you have a very low Z-score (more than 2 standard deviations below other individuals your age), your doctor should consider whether other medical conditions or medications may be causing lower than expected bone density.

Although you may have low bone density when you have your first test, your doctor cannot tell if you have lost bone density or if you have always had lower bone density due to family or medical history. Your peak adult bone mass may have been below that of the average individual. For example, if you have a T-score of -2.5, it is not appropriate to say that you have lost 25% of your bone density unless you had a bone density test when you reached peak bone density. There are lab tests that can help your doctor determine if you are currently losing bone density.

Assessing your risk

Your bone density is only one of many factors that affect your bone health. Other factors include family history, medical conditions you have had and medicines you have taken. The American Bone Health Fracture Risk Calculator™ helps you identify other factors and calculates your 10-year fracture risk. This can help you with healthcare, lifestyle, and treatment choices.

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Posted: 12/5/2016; Revised: 08/14/20. 
As a service to our readers, American Bone Health provides access to our library of archived content. Please note the date of the last review on all articles. No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician.6/19/19

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What is densitometry, how is it performed, x-ray examination, preparation for the procedure – MEDSI

Densitometry is a method for diagnosing the density and likelihood of bone fractures. With the help of this analysis, the level of calcium, the general density and structure, the thickness of the surface layer of the bones are measured.

Thanks to this study, osteoporosis can be detected at an early stage and its treatment can be started in a timely manner. It also helps prevent calcium deficiency in the body of a pregnant woman, which is important for the proper development of the fetus.

Principle and types of examination

Depending on which part of the body and under what conditions it is necessary to examine, different examination options can be applied. It is possible not only to examine the bones of the pelvis, spine or limbs, but also densitometry of the teeth.

Ultrasound examination

The examination device emits ultrasonic waves with a frequency greater than 3 MHz. In the process, the speed of the wave passing through the bone tissue varies depending on its density.

All changes in this speed are recorded and then used for diagnosis and comparison with normal values.

This procedure is completely painless and harmless and is suitable for pregnancy or other radiation restrictions.

X-ray examination

This method is based on the use of X-ray radiation. It lingers in tissues with a dense mineralized structure.

The analysis can be used both for examination of the spine, lumbar and femoral regions, as well as for extremities: hands and feet.

This examination is highly accurate and enables visualization of the bone structure. It allows you to detect bone loss at an early stage.

The dose of radiation that the body receives in this case is low, but dangerous for pregnant women, since the rays can affect the normal development of the fetus.

Other types

Magnetic resonance imaging and computed tomography can also be used to diagnose osteoporosis.

A separate area is dental densitometry using radiovisiography (computer X-ray). Studies have shown that this type of analysis allows you to explore the degree of damage to the hard tissues of the tooth (dentin) by caries.

When is densitometry needed?

The doctor prescribes this type of examination for the following symptoms:

• Frequent bone fractures, especially of the femur
• Fractures, dislocations associated with the spine
• Regular back pain of unknown cause
• Diseases of the gastrointestinal tract, kidneys, liver
• Diabetes mellitus

There are also a number of diseases in which densitometry is recommended:

• Metabolic disorders associated with the removal of calcium and phosphorus from the body
• Neurological diseases
• Long-term hormonal treatment
• Previously diagnosed osteoporosis
• Disorders of the endocrine system

For prophylactic purposes, different types (including dental densitometry) of this test are used in such cases:

What are the contraindications?

There are not many of them and they are related to the type of densitometry used:

• When the patient is pregnant, X-ray examination should not be used
• Pain or disturbance in the lumbar region, due to which the patient will not be able to lie still for at least half an hour

Preparing for your procedure

There are a few simple steps you can take to prepare for your densitometry:

• A few days before your test, you should avoid foods high in calcium (such as cottage cheese)
• It is also necessary to stop taking medicines containing phosphorus and calcium for a while – it is worth consulting with your doctor about this

In case of existing limitations of the study, it is necessary to take into account their presence:

• The patient must inform the doctor about the pregnancy. In this case, she will be prescribed an examination using ultrasound waves, since X-rays harm the still developing organism
• If an MRI is to be performed, the physician should be warned of the presence of metal implants, as they may skew the results. And in the presence of some of them, it is absolutely impossible to conduct an MRI. In this case, the doctor will decide which type of study is better to prescribe
• The doctor must also be notified if, shortly before the given examination, the patient underwent:
• Radioisotope scanning
• Computed tomography with contrast agent
• X-ray with barium

In all these cases, the physician must determine when it is best to undergo an examination so that due to previous analyzes there is no distortion of the results or an excessive burden on the patient’s body.

All these rules apply to the dental densitometry procedure.

How densitometry is performed

A special device is used for examination – a densitometer. The process itself is as follows:

• The subject’s clothing should be loose so as not to interfere with the study
• The patient sits on a couch or table in a position that depends on the organ being examined (when scanning the spine – lying on the back, etc.)
• Sensor and detector placed above the area to be analyzed
• The vehicle moves along the study area, while transmitting data on reflected and absorbed waves
• The procedure lasts up to half an hour, during which the patient must be immobile
• All results are stored on the computer and can be used later

If one of the extremities (hands, feet) is examined, then for this purpose it is placed in a special cavity of the device. In this case, the procedure lasts much less – just a few minutes.

Interpretation of test results

Based on the results of the examination, the doctor receives two main types of data:

• T-score. Its value is formed from comparisons of bone density with an indicator in the norm – 1 point or more. If it is less than specified, then:
• Digit -1 to -2.5 – decrease in mineral density
• Below -2.5 – osteoporosis with a high probability of fractures
• Z-score. It is determined by comparing bone mass with the average norm for the age of the patient. A negative value is low bone density

Advantages of densitometry of teeth and other organs at MEDSI

• Anyone can make an appointment for a consultation easily and simply: by phone 8 (495) 7-800-500
• More than 20 clinics in different parts of Moscow are always ready to receive patients
• Highly qualified radiologists and diagnosticians provide a full range of services: prepare clients for examination, accompany the process and decipher data
• The use of modern high-quality equipment allows you to get the most accurate results and start treatment on time

Do not delay treatment, see a doctor now:

• Densitometry
• Treatment of osteoporosis
• Endocrinologist appointment

ABC-medicine

Densitometry is a method for measuring bone mineral density, that is, the content of calcium, which is its main structural element. The information obtained is subjected to computer processing, the thickness and dimensions of the bones, their bulk density are calculated. Such indicators make it possible to judge the resistance of bone tissue to mechanical stress. Of particular importance is the densitometry of the femoral neck, as well as the study of the spine, since fractures of these areas are considered the most dangerous and threaten loss of motor activity for a long period of time.

In Moscow, densitometry can be done at the clinics of the ABC-Medicine network. We use state-of-the-art equipment to ensure the most accurate results. The price of bone densitometry varies depending on the area of ​​study.

Indications for

• For women – over 65 years of age, for men – over 70 years of age.
• Leading an unhealthy lifestyle (alcohol and coffee abuse, smoking, exhausting or reduced physical activity).
• Pathologies of the endocrine system (various hormonal disruptions, infertility, late onset of the menstrual cycle, early menopause).
• Long-term hormone therapy.
• Overweight or underweight.
• Diseases of the gastrointestinal tract.
• Rheumatic diseases.
• Renal failure.
• Chronic liver disease.
• Hereditary osteoporosis.
• Fractures due to minor trauma.
• Diabetes and others

Bone densitometry is also a method for monitoring the effectiveness of the treatment of the above diseases.

Purpose of the procedure

• Assessing the risk of osteoporosis.
• Determination of bone mineral density.
• Evaluation of the effectiveness of therapy aimed at stopping bone demineralization.

How to perform the procedure

Before performing densitometry of the spine or other parts of the skeleton, the patient must remove all metal jewelry, as well as clothing with metal parts (buckles, buttons, etc.).

For densitometry, modern X-ray equipment is used – a densitometer. During the procedure, the patient is on a special table in the supine position (the legs should be straightened or the shins should be lowered down). Certain areas of the skeleton are scanned using X-rays, during which the sensor of the equipment measures the degree of absorption of the transmitted rays. Based on this information, a graph is built. With bone densitometry, the area of ​​​​the area under study and the content of mineral components are measured, and then, using the obtained data, the mineral density of bone tissues is calculated.

Densitometry is non-invasive, does not cause discomfort or pain to the patient, and has no side effects. The duration of the procedure depends on the amount of research. Usually densitometry of the lumbar spine or other parts of the skeleton takes 10-20 minutes.

Test results

Densitometry of the spine and femoral neck, as well as other parts of the musculoskeletal system, provides an image of the bones, information on bone mineral density, percentage of normal and indicators of deviation from it. The results of the study indicate the following two values.

• T-score (main). It shows how much the obtained value of bone density deviates from the reference value (the bone density in young people aged 20-29 is taken as the reference). The following results are possible here:
• Т > -1 – mineral density is normal;
• T \u003d from -1 to -2.5 – the density is below normal;
• T < -2.5 - development of osteoporosis.
• Z – point (auxiliary). It shows how much the received value deviates from the norm for people of your sex, age and body weight. If this indicator is less than zero, an additional medical examination is required to clarify the diagnosis.

Thanks to densitometry, the doctor can determine the risk of fractures, choose tactics for the treatment and prevention of osteoporosis. Examination after arthroplasty allows assessing the density of the bone around the prosthesis and its stability.