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St. Vincent's Medical Center, Bridgeport CT

Bone Density & Osteoporosis

Densitometry Test - Questions & Answers

St. Vincent's SWIM Women's Imaging Center (203) 576-5500

Like other organs in the body, bones are constantly changing. Throughout childhood and as young adults, bones grow in strength and size. Around the age of 30, bones reach their peak strength and then naturally become weaker with age.

Osteoporosis is a condition where bones become weak to the point of breaking. This weakening may be due to aging or caused by other factors that combine with age. Symptoms of osteoporosis do not occur until a lot of bone strength is lost.

The most visible symptoms may include loss of height along with curvature of the upper back. Osteoporosis also can result in a crippling and painful fracture, occurring most often in the hip, back or wrist.

Who is at risk?

Age is an important risk factor. Everyone, both men and women, loses bone strength as they grow older. Women have higher risk for osteoporosis than men do as women have smaller, thinner frames. Women also are affected by the change-of-life known as menopause. After menopause, women produce less of a hormone called estrogen. Estrogen helps protect women against bone loss.

Important risk factors for osteoporosis include 

  • female
  • Caucasian
  • advanced age
  • history of bone fracture
  • a small, thin frame
  • a family history of osteoporosis
  • removal of the ovaries
  • early menopause
  • a low calcium diet
  • lack of exercise
  • eating disorders
  • certain medicines (such as steroids or anticonvulsants)
  • alcohol and tobacco use


How do I know if I have osteoporosis?

Osteoporosis is often called the "silent disease." There are rarely signs until a lot of bone has been lost. A medical test that measures the amount of bone is the best way to detect osteoporosis. A bone densitometer is one such test. The bone densitometer uses small amounts of x-ray to measure the amount of bone mineral. The amount of bone mineral relates directly to bone strength.

What can I expect during my bone densitometry test?

The bone densitometer is like a large examination table. It is padded and comfortable. Your name, age, height, weight and ethnicity will be entered into the computer before your test. This information is used to compare your results to a normal reference group. You will be asked to lie on your back, remaining in your normal clothing in most cases. Belt buckles, metal or thick plastic buttons, and metal jewelry will need to be removed from the region being examined. The technologist will position your arms and legs for the test. The test is painless and typically takes around 15 minutes. You just need to lie still and breathe normally.

Is the test safe?

Even though x-rays are used, the amount absorbed by the patient is only about 1/10th of that received from a chest x-ray. Other x-ray procedures have even higher x-ray doses. The x-ray dose from the bone densitometry test is comparable to the naturally occurring radiation you are exposed to in one week.

CAUTION: Even though the x-ray dose from the bone densitometry test is very low, please inform the operator if you are pregnant or might be pregnant before your test!

What information will the test give my doctor?

A bone densitometry test is an aid to doctors in the diagnosis of osteoporosis. The test compares your bone mineral density (BMD) to that of a "young adult" at peak bone strength. It also compares your results to people of your same age, called "age-matched." This information, along with other factors, helps doctors gauge your risk of osteoporotic fracture. The difference between your result and that of a "young adult" is given as a T-score. A panel of experts at the World Health Organization (WHO) has developed categories that define the amount of bone loss: 

  • Normal: a T-score that is above -1
  • Osteoporotic (low bone density): a T-score between -1 and -2.5
  • Osteoporosis: a T-score below -2.5 

Your T-score is one factor that your doctor will consider in making a diagnosis.

The bone densitometer test is also useful in following bone changes. The bone densitometer can monitor the effects of age, diet or treatment on your bone status. Your doctor may suggest follow-up tests to monitor change over time.

What is fracture risk? Why is it important to me?

The bone densitometry test provides information about your own risk of bone fracture in the same way a cholesterol test indicates risk of a heart attack. A diagnosis of osteoporosis cannot predict a bone fracture, just as high cholesterol cannot predict a heart attack. Instead, it means that the risk of having a fracture is higher than that for normal bones. Your test results, combined with other factors, will give your overall risk of fracture. Knowing your risk of fracture is important. There are a number of ways to prevent osteoporosis and to reduce your risk of fracture. Your doctor may suggest a number of steps including exercise, changes in diet, hormone therapy or other medicines known to build bone strength.

Are there other tests?

Bone densitometers provide information about fracture risk with an x-ray measurement of the spine, femur and wrist. Other tests include ultrasound to measure the status of the bone. Biochemical tests may be used for additional information in some cases.

Where can I get more information about bone measurements and osteoporosis?

The National Osteoporosis Foundation (NOF) is one of the leading sources of information about osteoporosis and bone measurements. The NOF recommends women have a bone density test if they meet the following criteria: 

  • You are over 65 years old
  • You are postmenopausal
    •  with >1 risk factor
    •  with a fracture You are considering osteoporosis therapy
  • You are on prolonged hormone replacement therapy  

The NOF recommends treatment if: 

  • You have a T-score <-1.5 with risk factors
  • You have a T-score <-2 with no risk factors
  • You are postmenopausal with a fracture   

Contact the NOF at: 

National Osteoporosis Foundation (NOF)
1150 17th St. N.W., Suite 500
Washington, D.C. 20036-4603
(202) 223-2226

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St. Vincent's SWIM Women's Imaging Center (203) 576-5500

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