Bone Densitometry

Bone density tests are quick and painless and provide information to your doctor about the health of your bones. While normal bone is dense and, therefore, strong, bone with osteoporosis is thinner, more porous, and more likely to break. When you have a bone density test, the results of the results are compared with the average bone mass of healthy adults with peak bone mass, as well as to adults of your same age and ethnicity. By following the bone loss over time, your doctor can determine if it is decreasing at an abnormally fast rate that might indicate osteoporosis. If low bone density is discovered, treatment can be started and additional bone density tests will track the progress.

Bone density is affected by heredity, diet, sex hormones, physical activity, lifestyle choices, and the use of certain medications. By age thirty, bone has typically reached its highest density and will then begin to gradually weaken, or lose density. In women, this loss is very gradual until menopause when the loss accelerates. One third of the total lifetime bone loss can occur in the first five years after menopause. For this reason, bone density tests are most frequently performed in women over 65. Women with histories that indicate a potential for osteoporosis (or that went through menopause early) should be tested younger. Although women develop osteoporosis four times more often than men, men can also develop the disease and should also be tested.

How bone densitometry works

Types of BMD Tests
There are central machines that measure density in the hip, spine and total body and peripheral machines that measure density in the finger, wrist, kneecap, shin bone and heel. During the test either a very small amount of radiation (about one tenth the dosage of a chest x-ray) or sound waves are used to determine the bone density of the spine, hip, finger, wrist, or heel.

• Dual Energy X-ray Absorptiometry measures the spine, hip or total body
• Peripheral Dual Energy X-ray Absorptiometry measures the wrist, heel or finger
• Single Energy X-ray Absorptiometry measures the wrist or heel
• Quantitative Ultrasound uses sound waves to measure density at the heel, shin bone and kneecap
• Quantitative Computed Tomography most commonly used to measure the spine, but can be used at other sites
• Peripheral Quantitative Computed Tomography measures the wrist
• Radiographic Absorptiometry uses an X-ray of the hand and a small metal wedge to calculate bone density
• Dual Photon Absorptiometry measures the spine, hip or total body (used infrequently)
• Single Photon Absorptiometry measures the wrist (used infrequently)

What to expect when you have the test:
Bone density tests can take anywhere from two to fifteen minutes. All methods of testing are noninvasive and safe. There is no pre-exam preparation needed, and you usually do not even have to change into a gown. You’ll simply relax, breathe normally, and let the machine scan the selected area. The RRA physician or technician will instruct you when the scan is complete.

The Results
The standard deviation result, established by the World Health Organization, may be the most useful and the easiest to interpret. Standard deviations indicate what is normal and what is not. Some experts say it’s best to look at the comparison to healthy young adults of your own ethnicity (called a T-score) because looking at your own age group (Z-score) may be comparing your bones with people who already have reduced bone density.

What do you look for in the T-score results?
A normal bone density will be within one standard deviation of a young adult, or plus or minus 1 SD. A score of 1 to 2.5 SD below the young adult (-1 SD to –2.5 SD) means the bone mass is low, and -2.5 SD and lower indicates osteoporosis. Your physician will determine the next steps based on these results. Bone building drugs and calcium can be used to reverse the effects of osteoporosis.