Originally published by Harvard Health.
What is the test?
This test, which is also called bone densitometry, uses specialized x-rays to measure the thickness and strength of your bones. Various scanners use different techniques. The one used most often is dual-energy x-ray absorptiometry (DXA). Quantitative ultrasound, which does not involve x-rays, may also be used.
When bones are somewhat thin, the condition is called osteopenia. When bones become very thin, the condition is called osteoporosis. Bone density tests provide a precise measure of whether you have osteopenia or osteoporosis.
Both sexes usually begin to lose bone thickness around age 50. However, women are much more likely than men to develop osteopenia and osteoporosis before age 70.
Exercise and various treatments can help prevent and even restore bone loss. That’s why diagnosing thin bones is important. Not only is a bone density test used to help detect osteopenia and osteoporosis. It’s also helpful in monitoring your progress if you’re taking bone-building medications.
How do I prepare for the test?
Be sure to tell your doctor if you might be pregnant. A screening test that uses x-rays can’t be performed during pregnancy because it may increase the risk of birth defects.
What happens when the test is performed?
Bone density tests can be done in the radiology department of a hospital, a radiology diagnostic center, or a doctor’s office. You lie on a table that has an overhanging cover, resembling a tanning bed, while a radiologist or x-ray technician moves a scanner above your spine, hip, or wrist. The test takes 10-20 minutes. The test itself is painless, but you may experience some discomfort because you have to lie still.
What risks are there from the test?
The test doesn’t have any significant risks. Bone density tests that use x-rays expose you to about one-tenth the amount of radiation as in a single chest x-ray. This is too small an amount to be likely to cause any harm, except to a fetus in a pregnant woman.
Must I do anything special after the test is over?
How long is it before the result of the test is known?
You’ll get the results within a few days. The results will include two scores, the T-score and the Z-score. The T-score measures your bone density compared with the average values in young adults of the same race and sex. The Z-score shows how your bone density compares with that of people your own age, race, and sex. A positive T-score means your bones are stronger than the average in a young adult, and a negative score means that your bones are weaker. If you have a T-score that is between -1.0 and -2.5, you have osteopenia. If it is below -2.5, you have osteoporosis.
In general, the lower your bone density, the higher your risk of breaking a bone. Fractures of the hip are particularly disabling, and fractures of the spine are common and painful. Bone density measured at the hip and spine by DXA is regarded by most experts as the best predictor of hip and spine fracture. DXA also is excellent for diagnosing thin arm bones; wrist fractures occur more easily in people with osteopenia or osteoporosis. Fortunately, treatment options exist. Talk with your doctor.