Bone Mineral Density Tests

Osteoporosis (or porous bone) is a disease in which bones become weak and are more likely to break. Without prevention or treatment, osteoporosis can progress without pain or symptoms until a bone breaks (fractures).

• Fractures commonly occur in the hip, spine, and wrist.



• Osteoporosis is the underlying cause of more than 1.5 million fractures annually (300,000 hip fractures, approximately 700,000 vertebral fractures, 250,000 wrist fractures, and more than 300,000 fractures in other areas). 



• The estimated national cost (hospitals and nursing homes) for osteoporosis and related injuries is $14 billion each year in the United States. 

Osteoporosis is not just an “old woman’s disease.” Although it is more common in white or Asian women older than 50 years, osteoporosis can occur in almost any person at any age. In fact, more than 2 million American men have osteoporosis, and in women, bone loss can begin as early as age 25 years. Building strong bones and reaching peak bone density (maximum strength and solidness), especially before the age of 30, can be the best defense against developing osteoporosis. Also, a healthy lifestyle can keep bones strong, especially for people older than 30 years.

Osteoporosis is more or less preventable for most people. Prevention is very important because, while treatments for osteoporosis are in place, currently no cure exists. Prevention of osteoporosis involves several aspects, including nutrition, exercise, lifestyle, and, most importantly, early screening with bone density tests.

The importance of screening for osteoporosis

Early detection of low bone mass (osteopenia) or osteoporosis is the most important step for prevention and treatment. If osteopenia or osteoporosis has occurred, a person can take action to stop the progression of bone loss. Remember, effective treatment or prevention cannot take place if a person does not know he or she has, or is at risk for, osteoporosis.

The only way to accurately test the strength and solidness of the bones is with bone mineral density (BMD) tests. Bone mineral density tests measure the solidness and mass (bone density) in the spine, hip, and/or wrist, which are the most common sites of fractures due to osteoporosis. Other tests measure bone density in the heel or hand. These tests are performed like x-rays. They are painless, noninvasive, and safe. The risk of radiation is very minimal, much less than even having a chest x-ray film.

Risk factors for osteoporosis

Certain factors are associated with an increased risk of developing osteoporosis (see Prevention of Osteoporosis). Take a 1-minute osteoporosis risk test from the International Osteoporosis Foundation. 

If a person has any of these risk factors or other signs of osteoporosis, a doctor may recommend that bone mass is measured. Risk factors for osteoporosis include the following:

• Advancing age



• Early menopause (age <45 years)



• Female sex



• Asian or white race



• Family history of hip fracture



• Low body weight



• Long-term corticosteroid therapy  



• Chronic disorders associated with osteoporosis, such as anorexia nervosa or liver disease



• Previous broken bones with minimal trauma 



• Poor diet without enough calcium



• Lack of exercise



• Smoking

Current recommendations

According to current recommendations in the United States by the National Osteoporosis Foundation, the following individuals should have a bone mineral density test:

• All women 65 years and older, regardless of risk factors



• Younger postmenopausal women who have one or more risk factors (other than being white, postmenopausal, and female)



• Postmenopausal women who present with fractures (to confirm the diagnosis and determine disease severity)

Medicare and bone mineral density testing

• Medicare covers bone mineral density testing for the following individuals 65 years and older:
  
  

  • Women with low estrogen levels who have risk factors for osteoporosis

  • Men and women with abnormalities of the spine (vertebral abnormalities)

  • Men and women who are receiving (or are going to receive) long-term steroid (glucocorticoid) therapy

  • Individuals with primary hyperparathyroidism

  • Men and women on drug therapy for osteoporosis who are being monitored to determine the effectiveness of the drug therapy

• Medicare permits individuals to repeat bone mineral density testing every 2 years.

Bone mineral density tests measure the solidness and mass (bone density) in the spine, hip, and/or wrist (the most common sites of fractures due to osteoporosis). Some bone mineral density tests measure bone in the heel or hand. These tests are performed like x-ray films, and they are the only reliable way to determine loss of bone mass. They are painless, noninvasive, and safe. 

Doctors examine bone mineral density test results to do the following:

• Detect low bone density (osteopenia) before a fracture occurs



• Confirm a diagnosis of osteoporosis if a person already has broken bones (fractures)



• Predict the chance of a person having a fracture in the future



• Determine the rate of bone loss and monitor the effects of treatment (tests performed to monitor treatment are usually conducted every year or so)

Several tests are available to assess bone density. These tests are not painful, and they are completely noninvasive, which means no surgery. Central machines measure density in the hip, spine, and total body. Peripheral machines measure density in the finger, wrist, kneecap, shinbone, and heel. The most common types of tests are listed below:

• Dual energy x-ray absorptiometry (DXA or DEXA) scanning is a special low-radiation x-ray that can detect bone loss—even very small amounts of bone loss. DXA scans are the most commonly used method of bone mineral density measurement. They are used to measure spine and hip bone densities. Peripheral dual energy x-ray absorptiometry (pDXA) measures the bone density in the forearm, finger, and heel. Single-energy x-ray absorptiometry (SXA) measures the bone density in the wrist or heel.



• Quantitative computed tomography (QCT) scanning measures the bones of the lower spine because these bones change as a person ages. The peripheral QCT scan measures the forearm bone density.



• Quantitative ultrasound (QUS) uses sound waves to measure bone density at the heel, shin, and finger.



• Radiographic absorptiometry (RA) scanning uses an x-ray film of the hand and a small metal wedge to calculate bone density. 

Bone mineral density tests measure bone density in the spine, hip, and/or wrist, which are the most common sites of fractures due to osteoporosis. The results of the bone mineral density test are compared to 2 standards (norms):

• The age-matched reading, known as the Z-score, compares a person's bone density to what is expected in someone of equivalent age, sex, and size. However, among older and elderly adults, low bone mineral density is common, so comparison with age-matched norms can be misleading. 



• The young-normal reading, known as the T-score, compares bone density to the optimal peak bone density of a healthy young adult (30 years old) of the same sex. The T-score determines fracture risk, which increases as bone mineral density falls below young-normal levels. The T-score, which is a comparison between the solidness (density) of the bones and the bones of the average young healthy population, is measured in standard deviations (SDs). SD is a statistical term that describes variation in a population. According to the World Health Organization’s (WHO) diagnostic categories, individuals whose T-score is within 1 SD of the norm are considered to have normal bone density. Scores below the norm are indicated in negative numbers. For most bone mineral density tests, -1 SD equals a 10-12% decrease in bone density. The risk for broken bones increases by 50-100% for every SD below the young-normal standard.

WHO definitions of osteoporosis based on bone density levels

• Normal: Bone density is within 1 SD (+1 or -1) of the young adult mean.



• Low bone mass (osteopenia): Bone density is 1 to 2.5 SDs below the young adult mean (-1 to -2.5 SD). 



• Osteoporosis: Bone density is 2.5 SDs or more below the young adult mean (> -2.5 SD).



• Severe (established) osteoporosis: Bone density is more than 2.5 SDs below the young adult mean and one or more broken bones (osteoporotic fractures) has occurred.

With the information from a bone density test, a doctor can identify the degree of bone loss and determine whether a person is at risk for fracture. In general, the lower the bone density (weaker bones), the higher the risk for fracture. Test results help determine which prevention or treatment options are right.

National Osteoporosis Foundation
1232 22nd Street NW
Washington, DC 20037-1292
(202) 223-2226

International Osteoporosis Foundation
info@osteofound.org

National Institutes of Health Osteoporosis and Related Bone Diseases National Resource Center
2 AMS Circle
Bethesda, MD 20892-3676
(800) 624-Bone
niamsboneinfo@mail.nih.gov

|Web Links|

NIH Osteoporosis and Related Bone Diseases–National Resource Center, Osteoporosis Fact Sheets 

National Osteoporosis Foundation, Osteoporosis, Bone Density

Osteoporosis Explained

Yahoo Health, Osteoporosis Health Center

Media file 1: The image on the left shows decreased bone density in osteoporosis. The image on the right shows normal bone density.

Media type:  Illustration

Media file 2: Arrow indicates vertebral fractures.

Media type:  Illustration

Media file 3: A. Normal spine, B. Moderately osteoporotic spine, C. Severely osteoporotic spine.

Media type:  Illustration

osteopenia, weak bones, porous bones, bone loss, bone density loss, bone mineral density loss, BMD, dual-energy x-ray absorptiometry, DXA, DEXA, calcium and osteoporosis, menopause, hunchback, hump back, dowager’s hump, broken hip, T-score, T score, Z-score, Z score, quantitative computed tomography, QCT, quantitative ultrasound, QUS, bone mineral density tests

Author: Mythili Seetharaman, MD, Consulting Staff, Department of Rheumatology, Albert Einstein Medical Center.

Coauthor(s): Jessica B Johnson, Medical Writer, .com, Inc.

Editors: Kristine M Lohr, MD, Associate Chief, Program Director, Professor, Department of Internal Medicine, Division of Rheumatology, University of Tennessee School of Medicine; Mary L Windle, Pharm D, Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Pharmacy Editor, .com, Inc; Rick Kulkarni, MD, Assistant Professor of Medicine, David Geffen UCLA School of Medicine; Director of Informatics, Department of Emergency Medicine, UCLA/Olive View-UCLA Medical Center.