Body Composition Testing Q &A
How is the body composition test done?
Your body composition will be determined by a test called dual-energy x-ray absorptiometry (abbreviated as
DXA). This is a type of low-dose x-ray that is able to determine the amount of different types of tissues in
your body.
What does DXA measure?
DXA measures the total amount of three types of tissue in your body:
•
The amount of mineral in your bones (called bone mineral content, abbreviated as BMC)
•
Lean tissue (which is mostly muscle but includes ligament, tendons, and body organs like heart, lungs,
liver, and bowels)
•
Fat
For most people, the measurement of interest is the amount of fat. DXA determines the total amount of fat in
your body and expresses this as a percentage of you total body weight. This is referred to as % body fat.
How long does the appointment take?
The DXA test takes less than 10 minutes. The entire appointment is approximately 20 minutes.
What is involved in the DXA test?
To have a DXA test, you simply lie on a padded table. A small arm of the DXA machine gradually passes over
you to measure your body components. The machine is not closed-in like an MRI machine or CT machine, so
there are no concerns for those with claustrophobia. Your feet will be placed in a brace so that your legs are
held in a specific position. You will be required to lie still for the entire procedure (7 to 10 minutes). This
might be uncomfortable for some people, but other than this, there is no discomfort in the test. No injections
are involved.
What should I wear?
Any metal objects on clothing (like zippers, buttons, clasps, belt buckles, or wire on underwire bras) or
jewelry will interfere with the measurements. It is best to avoid these. The best clothing is something like
sweat pants and t-shirt with no metal. If you are unable to wear clothing such as this to your appointment, a
gown will be provided to change into. You will be asked to remove all jewelry. Small jewelry like navel rings
is acceptable if it cannot be removed as the effect on the test will be minimal.
Is there any other preparation for the test?
No other preparation is required.
Are there any possible complications from the DXA test?
No.
How high is the radiation dose I will receive?
The amount of radiation from a DXA test is considered small. It is about 1/10 the amount you would receive
from a chest x-ray.
Are there any reasons I cannot get a DXA test?
Some other kinds of x-rays can interfere with the DXA test if done in the weeks before the DXA. If you have
had a nuclear medicine test or x-ray dye for a CT scan in the prior week, or have had a barium drink or
barium enema x-ray in the prior two weeks, you should reschedule the DXA test. If you are a woman who is
pregnant you cannot have the test. If you are a woman who might be pregnant, you need to make sure that
you are not pregnant before doing the test.
What if I have had a hip or knee replacement?
If you have had metal placed in the body during surgery, including artificial joints or spine supports, you can
still have a DXA test. The metal will have some effect on the accuracy of the assessments for the tissue
types in your body, but the effect on the fat measurements is usually very small.
Does the test tell whether I have too little calcium in my bones?
The DXA test measures the amount of mineral in your entire skeleton, which reflects the calcium content of
your bones. Low amounts of mineral are usually due to a condition called osteoporosis. This condition
affects certain bones more than others. The measurement of your whole skeleton is not the best way to
diagnose osteoporosis. If there is a concern about osteoporosis, it is better to do a different type of DXA test
that specifically measures the amount of mineral in your spine and hip.