Wednesday, May 1, 2013

BMD - Bone mineral density test and Osteoporosis - overview

Bone mineral density test

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A bone mineral density (BMD) test measures how much calcium and other types of minerals are in an area of your bone.

This test helps your health care provider detect osteoporosis and predict your risk of bone fractures.

How the Test is Performed

Bone density testing can be done several different ways.

The most common and accurate way uses a dual-energy x-ray absorptiometry (DEXA) scan. It uses low-dose x-rays. (You receive more radiation with a chest x-ray.)

There are two different types of DEXA scans:

  • Central DEXA. You lay on a soft table, and the scanner passes over your lower spine and hip. Usually, you do not need to undress. This scan is the best test to predict your risk of fractures.
  • Peripheral DEXA (p-DEXA). These smaller machines measure the bone density in your wrist, fingers, leg, or heel. These machines are in doctor's offices, pharmacies, shopping centers, and at health fairs.

How to Prepare for the Test

If you are or could be pregnant, tell your health care provider before this test is done.

How the Test Will Feel

The scan is painless. You will need to remain still during the test.

Why the Test is Performed

Bone mineral density (BMD) tests are used to:

  • Diagnose bone loss and osteoporosis
  • See how well osteoporosis medicine is working
  • Predict your risk of future bone fractures

You should have bone mineral testing or screening if you have an increased risk of osteoporosis. You are more likely to get osteoporosis if you are:

  • A woman over 65
  • A man over age 70

Women under age 65 and men ages 50 - 70 are at increased risk of osteoporosis if they have:

  • A broken bone caused by normal activities, such as a fall from standing height or lower (fragility fracture)
  • Chronic rheumatoid arthritischronic kidney disease, eating disorders
  • Early menopause (either from natural causes or surgery)
  • History of hormone treatment for prostate cancer or breast cancer
  • Significant loss of height due to compression fractures of the back
  • Smoking
  • Strong family history of osteoporosis
  • Taking corticosteroid medications (prednisone, methylprednisolone) every day for more than 3 months
  • Three or more drinks of alcohol per day on most days

Normal Results

The results of your test are usually reported as a T-score and Z-score.

  • T-score compares your bone density with that of healthy young women.
  • Z-score compares your bone density with that of other people of your age, gender, and race.

With either score, a negative number means you have thinner bones than the standard. The more negative the number, the higher your risk of a bone fracture.

A T-score is within the normal range if it is -1.0 or above.

What Abnormal Results Mean

Bone mineral density testing does not diagnose fractures. Along with other risk factors you may have, it helps predict your risk of having a bone fracture in the future. Your doctor will help you understand the results.

  • T-score between -1 and -2.5 indicates the beginning of bone loss (osteopenia).
  • T-score below -2.5 indicates osteoporosis.

Treatment recommendation depends on your total fracture risk. This risk can be calculated using the FRAX score. Your health care provider can tell you more about this. You can also find information about FRAX online.

Risks

Bone mineral density uses a slight amount of radiation. Most doctors feel that the risk is very low compared with the benefits of finding osteoporosis before you break a bone.

Considerations

Simple bone density scans using portable machines are often available as part at health fairs or screenings. These portable scanners check the bone density at your wrist or heel. Keep in mind that hip and spine scans are more reliable.

If you are diagnosed with osteopenia or osteoporosis:

  • Keep your bones strong by doing regular weight-bearing exercise such as brisk walking, tennis, or yard work.
  • Exercise such as tai chi improves balance and reduces risk of falls.
  • Check your home for fall hazards, such as loose rugs, to help reduce the risk of falls and fractures.

Alternative Names

BMD test; Bone density test; Bone densitometry; DEXA scan; DXA; Dual-energy x-ray absorptiometry; p-DEXA

References

Lim LS, Hoeksema LJ, Sherin K; ACPM Prevention Practice Committee. Screening for osteoporosis in the adult U.S. population: ACPM position statement on preventive practice. Am J Prev Med. 2009;36:366-375.

National Osteoporosis Foundation. Clinician's Guide to Prevention and Treatment of Osteoporosis. Washington, DC: National Osteoporosis Foundation; 2008.

U.S. Preventive Services Task Force. Screening for osteoporosis: recommendation statement. Am Fam Physician. 2011 May 15;83(10):1197-200.

Update Date: 11/8/2012

Updated by: Susan Storck, MD, FACOG, Chief, Eastside Department of Obstetrics and Gynecology, Group Health Cooperative of Puget Sound, Bellevue, Washington; Clinical Teaching Faculty, Department of Obstetrics and Gynecology, University of Washington School of Medicine. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, David R. Eltz, Stephanie Slon, and Nissi Wang.


Osteoporosis - overview

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Osteoporosis is a disease in which bones become fragile and more likely to fracture. Usually the bone loses density, which measures the amount of calcium and minerals in the bone.

Causes

Osteoporosis is the most common type of bone disease.

Because of osteoporosis about half of all women over the age of 50 will have a fracture of the hip, wrist, or vertebra (bone of the spine) during their lifetime.

Bone is living tissue. Existing bone is constantly being replaced by new bone. Osteoporosis occurs when the body fails to form enough new bone, when too much existing bone is reabsorbed by the body, or both.

Calcium is one of the important minerals needed for bones to form. If you do not get enough calcium and vitamin D, or your body does not absorb enough calcium from your diet, your bones may become brittle and more likely to fracture.

Sometimes bone loss occurs without any cause. Caucasian women are more likely to have bone loss. Sometimes the tendency to have bone loss and thin bones is passed down through families.

OsteoporosisWatch this video about:Osteoporosis

A drop in estrogen in women at the time of menopause and a drop in testosterone in men is a leading cause of bone loss. Other causes of bone loss include:

  • Being confined to a bed
  • Certain medical conditions
  • Taking certain medicines

Other risk factors include:

  • Absence of menstrual periods (amenorrhea) for long periods of time
  • A family history of osteoporosis
  • Drinking a large amount of alcohol
  • Low body weight
  • Smoking

Symptoms

There are no symptoms in the early stages of osteoporosis. Many times, people will have a fracture before learning that they have the disease.

Pain almost anywhere in the spine can be caused by fractures of the bones of the spine. These are calledcompression fractures. They often occur without an injury. The pain occurs suddenly or slowly over time.

There can be a loss of height (as much as 6 inches) over time. A stooped posture or kyphosis (also called a dowager's hump) may develop.

Exams and tests

Bone mineral density testing (most often with a DEXA scan) measures your bone mineral density. Your health care provider uses this test to:

  • Diagnose bone loss and osteoporosis
  • Predict your risk of future bone fractures
  • See how well osteoporosis medicine is working

spine or hip x-ray may show fracture or collapse of the spinal bones. However, simple x-rays of other bones are not very accurate in predicting whether you are likely to have osteoporosis.

You may need other blood and urine tests if your osteoporosis is thought to be due to a medical condition, rather than simply the usual bone loss seen with older age.

Treatment

Treatment for osteoporosis may involve:

  • Lifestyle changes, such as diet and exercise
  • Taking calcium and vitamin D
  • Using medicines

Medicines are used to strengthen bones when:

  • Osteoporosis has been diagnosed by a bone density study, whether or not you have a fracture.
  • A bone fracture has occurred and a bone density test shows that you have thin bones, but not osteoporosis.

Medicines used to treat osteoporosis include:

  • Bisphosphonates (the main drugs used to prevent and treat osteoporosis in postmenopausal women)
  • Estrogens, teriparatide, raloxifene, and calcitonin

Exercise plays a key role in preserving bone density in older adults. Some of the exercises recommended to reduce your chance of a fracture include:

  • Weight-bearing exercises -- walking, jogging, playing tennis, dancing
  • Free weights, weight machines, stretch bands
  • Balance exercises -- tai chi, yoga
  • Rowing machines

Avoid any exercise that presents a risk of falling. Also, do not do high-impact exercises that can cause fractures in older adults.

Your body needs calcium and vitamin D to keep your bones strong. Vitamin D helps your body absorb calcium.

  • Adults under age 50 should have 1,000 mg of calcium and 400 - 800 IU of vitamin D daily.
  • Women ages 51 to 70 should have 1,200 mg of calcium and 400 - 800 IU of vitamin D a day; men ages 51 to 70 need 1,000 mg of calcium and 400 - 800 IU of vitamin D a day.
  • Adults over age 70 should get 1,200 mg of calcium and 800 IU of vitamin D daily. 
  • Your doctor may recommend a calcium supplement.
  • Follow a diet that provides the proper amount of calcium and vitamin D.

Stop unhealthy habits:

  • Quit smoking, if you smoke.
  • Limit your alcohol intake. Too much alcohol can damage your bones. This puts you at risk of falling and breaking a bone.

It is important to prevent falls. The following are suggestions on how to do this:

  • Do not take sedating medicines, which can make you drowsy and unsteady. If you must take them, be extra careful when you are up and about. For example, hold on to countertops or sturdy furniture to avoid falling.
  • Remove household hazards, such as throw rugs, to reduce the risk of falls.
  • Leave lights on at night so you can see better when walking around your house.
  • Install and use safety grab bars in the bathroom.
  • Make sure your vision is good. Have your eyes checked once or twice a year by an eye doctor.
  • Wear shoes that fit well and that have heels. This includes slippers. Slippers that do not have heels can cause you to trip and fall.
  • Do not walk outdoors alone on icy days.

Surgery to treat severe, disabling pain from spinal fractures due to osteoporosis include:

Outlook (Prognosis)

Medicines to treat osteoporosis can help prevent future fractures. But spine bones that have already collapsed cannot be reversed.

Osteoporosis can cause a person to become disabled from weakened bones. Hip fractures are one of the main reasons people are admitted to nursing homes.

Prevention

Calcium is important for building and maintaining healthy bone. Vitamin D is also needed because it helps your body absorb calcium. Following a healthy, well-balanced diet can help you get these and other important nutrients.

Other tips for prevention:

  • Do not drink large amounts of alcohol.
  • Do not smoke.
  • Get regular exercise.

Medicines can prevent osteoporosis. Your doctor can tell you if any are right for you.

Alternative Names

Thin bones; Low bone density

References

Lewiecki EM. In the clinic. Osteoporosis. Ann Intern Med. 2011;155(1):ITC1-1-15;quiz ITC1-16.

National Osteoporosis Foundation. Clinician's Guide to Prevention and Treatment of Osteoporosis. Washington, DC: National Osteoporosis Foundation; 2010.

North American Menopause Society. Management of osteoporosis in postmenopausal women: 2010 position statement of The North American Menopause Society. Menopause. 2010 Jan-Feb;17(1):25-54.

Park-Wyllie LY, Mamdani MM, Juurlink DN, Hawker GA, Gunraj N, Austin PC, et al. Bisphosphonate use and the risk of subtrochanteric or femoral shaft fractures in older women. JAMA. 2011;305(8):783-789.

Update Date: 11/15/2012

Updated by: C. Benjamin Ma, MD, Assistant Professor, Chief, Sports Medicine and Shoulder Service, UCSF Department of Orthopaedic Surgery. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, David R. Eltz, Stephanie Slon, and Nissi Wang.

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