Is it a DEXA or DXA?
The DEXA (DXA) scan measures bone mineral density, which is often abbreviated as BMD. The scan uses invisible beams of energy to calculate the strength of your bones and helps diagnose osteoporosis. With these results, your risk of developing a broken bone, or fracture, can be determined. DEXA is an abbreviation for Dual Energy X-ray Absorptiometry. Dual Energy X-ray Absorptiometry is also shortened to DXA, which is considered to be the newer and correct way to abbreviate it.
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What does Dual Energy X-ray Absorptiometry (DEXA, DXA) mean?
Let’s break this term down into its individual parts:
DUAL ENERGY
Dual Energy means the test uses two types of energy. One energy beam is absorbed best by the softer tissues around the bone (like muscle and fat), while the second beam is absorbed by the bone itself.
X-RAY
An X-ray is an invisible wave of energy that passes through the tissues of the body. X-rays are painless and you cannot feel them.
ABSORPTIOMETRY
Absorptiometry refers to the amount of energy that is absorbed by the tissue and not allowed to pass through it.
In summary, the DEXA (DXA) test uses two types of invisible X-ray beams to measure how strong the bone is by studying the amount of energy it absorbs.
DEXA scan procedure
The DEXA (DXA) scan is usually performed on the hip and lower (or lumbar) spine, but can also include the non-dominant forearm. Images are taken while you lie on a large, flat table usually made of glass. The exam does not require you to move. Instead, the scanner moves over the top of you. When examining and taking X-ray pictures of the lower (or lumbar) spine, the technician will place a soft, cushioned box under your legs. The box is strong enough to support supports your legs fully and helps flatten your spine for better pictures.
To determine the bone density of the hips, the technician will place your foot into a brace that rotates it slightly toward your other foot. This rotation allows the hip to be in a position for the best picture. When you are positioned correctly and the test is about to begin, the technician will inform you that they are about to activate the machine. The machine is turned on after the operator steps behind a protective wall or into the next room.
The bone density test will take about 15 to 30 minutes.
What is the cost of a DEXA scan?
The costs of medical tests can vary widely depending on where you live and your insurance coverage. The typical cost of a bone density test for patients without health insurance ranges from $150 to $250. Discuss the fees with the facility staff and with your insurance provider.
DEXA scan side effects - How much radiation is there with a DEXA scan?
The DEXA (DXA) scan is a painless test and is considered to be a simple and quick study. Think of it like having an X-ray (with far less radiation). For some patients, the most challenging thing about undergoing this test can be lying flat for a short period of time. As a rule, bone mineral density machines use very low radiation doses. The radiation dose from older machines, which use a skinny, pencil beam, are lower than newer ones that use a fan beam for higher resolution pictures.
It was once thought that the dose of radiation from completing a DEXA (DXA) scan was about one-tenth. However, newer studies suggest the radiation exposure to the patient undergoing a DEXA scan is much lower—up to 200 times less than someone going for dental X-rays! It is important to tell the technician if you are pregnant before undergoing a DEXA (DXA) scan, because X-rays can be dangerous to a developing baby.
What are the DEXA scan guidelines?
Medicare is considered the authority in determining when a bone mineral density test will be covered by insurance. There are several different task forces that have set guidelines on when DEXA studies should be performed. The most important are the United States Task Force, the National Osteoporosis Foundation and the International Society for Clinical Densitometry.
It is agreed that bone density tests should be performed for the following patients:
Women age 65 or older
Women younger than 65 with risk factors causing their fracture risk to be equal to or greater than a 65-year-old Caucasian woman
Bone density testing should be strongly considered for the following patients:
Men age 70 or older
Men age 50-69 with risk factors (low body weight, high-risk medications, medical conditions associated with low bone mass)
Adults older than 50 with an adult-age fracture
How often bone mineral density testing should be repeated depends upon the specific needs of individual patients. In general, repeat testing is performed every two years, but this recommendation is based more on insurance coverage than evidence. If you are on a medication to treat osteoporosis, the National Osteoporosis Foundation recommends a bone density test every one to two years. Discuss your individual needs with your physician.
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DEXA scan preparation - What happens if I take calcium before a DEXA scan?
Calcium supplements should not be taken for 24 hours before your bone density test. Because the spine lies behind the stomach, undigested calcium in the stomach can give false readings about the bone density in the spine. Calcium supplements include things you might not know have calcium, like your multivitamin and antacids like Tums® and Rolaids.
How should I prepare the night before or morning of the test?
What to expect when you arrive for your bone density procedure.
On the day of your procedure, after registering at the front desk, expect to meet a technician with experience in performing bone density testing. Be sure to tell the technician if you recently underwent any other radiology testing. It is most important to mention tests that required you to swallow contrast, such as computerized tomography CAT or CT scans. If this is true in your case, you will need to wait about two weeks before completing the bone density scan. Before undergoing the DEXA, you will be asked to fill out a questionnaire. Your answers help the technician enter your information correctly into the software (computer program). This personal information is extremely important, as it will help determine your FRAX score, which measures your risk of developing a fracture. using a tool called the FRAX score.
You should be prepared to answer at the least the following questions:
DEXA scan results and interpretation
The DEXA (DXA) scan is the only test that can diagnose osteoporosis before a broken bone occurs. Typically, a radiologist—a doctor who specializes in reading imaging studies—will interpret the results of your bone density. Rarely, an endocrinologist (gland doctor) or rheumatologist (joint specialist) will be reviewing your test. With newer software, the results are automated by the computer after the technician takes the pictures at very specific levels or areas within your bones.
The test results provide four important pieces of information:
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Your bone mineral density (g/cm2)
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Your T-score. A T-score shows how much higher or lower your bone density is compared to a healthy, 30-year-old adult of your sex.
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Your Z-score. A Z-score compares your bone density to someone of your sex, age, size, and ethnicity. This score is considered useful for patients under the age of 50.
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Any change from an earlier study, if one was previously done at that center.
A T-score of -1.0 or above is considered normal bone density. A T-score between -1.0 and -2.5 is called low bone density or osteopenia. A T-score of -2.5 or below is called osteoporosis.
If you are planning to repeat your bone density test, it is important to use the same scanner each time. If this is not possible, try to use a machine made by the same company. There can be very large errors when trying to compare the measurements from studies done on different machines.
What about a DEXA scan for body fat?
A DEXA (DXA) scan can also be performed to determine body fat percentage. The DEXA scan is considered the gold standard to examine what doctors call body composition, or how much fat your body contains (% body fat).
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