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Bone Density Scan

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.

Certain treatments for pediatric cancer can cause loss of bone mass, which can later result in osteoporosis.

Current patients and childhood cancer survivors who are at risk of bone mass loss include patients who:

  • Have a condition that can weaken the bones
  • Take medicine that can weaken bones
  • Are getting treatment for bone problems

Childhood cancer survivors at risk for developing osteoporosis should have a DXA scan when they enter long-term follow-up care.

How to Prepare for a DXA Scan

Medical and treatment history

Parents will likely be asked to complete a questionnaire about the patient’s bone health history and previous medical treatments.

Important things to tell the staff ahead of time

  • Tell the staff if the patient recently had an exam or scan with barium or contrast liquid. If the answer is yes, the procedure may be rescheduled.
  • Tell the staff if there is a chance the patient could be pregnant. If she is, the test could hurt the baby.

Stop calcium supplements

Patients who take medicines with calcium or calcium supplements (such as daily vitamins) should stop taking them at least 24 hours before the scan. 

Wear comfortable clothes

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:

  • Watches
  • Jewelry
  • Hair clips with metal
  • Glasses
  • Dental retainers with metal in them

Patients might wear a hospital gown during the scan. 

Patient should stay still

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.

What to Expect During a DXA Scan

  • The patient lies on a padded table while the scanner moves over his or her body.
  • A DXA scan usually takes pictures of the spine and hips but sometimes scans the whole body.
  • For a scan of the spine, a staff member will put the patient’s legs on a padded box to keep the back flat.
  • For a scan of the hip, a staff member will put the patient’s foot in a brace. These adjustments help the scanner get the best pictures.
  • The patient might hear a humming noise from the scanner, but scans are not usually very noisy.
  • The scan does not hurt.

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.

Young African-American patient prepares to undergo a bone density scan with technologist nearby.

For a scan of the spine, a staff member will put the patient’s legs on a padded box to keep her back flat.

Are DXA scans safe for my child?

A DXA scan uses much less radiation than a regular X-ray. Parents should discuss any concerns with the medical team.

Will someone be with the patient during the scan?

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.

When will families receive results, and what do they mean?

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