My Bone Densitometry Test
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 does the densitometer work?
The bone densitometer uses small amounts of x-ray to produce images of the spine, hip or even the whole body. The x-ray is composed of two energy levels which are absorbed differently by the bones in the body. The technical term for the method is "dual-energy x-ray absorptiometry," or DEXA. A computer is able to determine from these differences how much bone mineral is present. The spine and hip are measured because that is where osteoporotic fractures occur most.
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 operator will position your arms and legs for the test, which is painless and typically takes one to ten 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
Osteopenic: (low bone density) a T-score between -3 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 densitometry test is also useful in following bone changes. The
bone densitometer can monitor the effects of age, diet, or treatments
on your bone status. Your doctor may suggest follow-up tests to monitor
change over time.