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A bone mineral density test measures bone mass. Bone mineral density refers to the amount of calcium and other bone minerals in bone. The most commonly used bone mineral density test is DXA or DEXA (dual energy X-ray absorptiometry), which uses X-rays to measure bone mass.
Current patients and childhood cancer survivors who are at risk of bone mass loss include patients who:
Childhood cancer survivors at risk for developing osteoporosis should have a DXA scan when they enter long-term follow-up care.
Parents will likely be asked to complete a questionnaire about the patient’s bone health history and previous medical treatments.
Patients who take medicines with calcium or calcium supplements (such as daily vitamins) should stop taking them at least 24 hours before the scan.
Patients should wear loose, comfortable clothes with no metal snaps or zippers because metal shows up on bone density tests.
Other items to avoid are:
Patients might wear a hospital gown during the scan.
A DXA scan takes about 45 minutes. The patient must remain still, or the X-rays will be blurry. It might help if the patient pretends to sleep or be a statue.
In rare cases, children may need medicine to help them lie still. In the case of infants, the staff might ask parents to feed them right before the exam.
The DXA machine sends low-dose X-rays with two different energy peaks through the bones being examined. Soft tissue mainly absorbs one peak. Bone mainly absorbs the other one. The soft tissue amount can be subtracted from the total. The remaining amount is the patient's bone mineral density. DXA scan machines feature special software that compute and display the bone density measurements on a computer monitor.
A DXA scan uses much less radiation than a regular X-ray. Parents should discuss any concerns with the medical team.
A parent can usually stay with the patient. (If pregnant, the parent will have to remain in the waiting room.)
A staff member will be nearby operating the machine.
A radiologist, a physician trained to interpret imaging tests, will analyze the results and send a report to the patient’s oncologist. It can take 1 day to several days to get DXA scan results. Ask the doctor when to expect them.
A DXA scan produces a measurement called a Z-score. This score shows how much bone mass the patient has compared to other people of the same age, size, and gender. If this score is unusually high or low, it may indicate a need for further medical tests.
Reviewed: July 2018