Bone Mineral Density

Studies show that men who receive hormone deprivation therapy for prostate cancer have an increased risk of developing osteoporosis and broken bones. Hormones such as testosterone protect against bone loss. So, once these hormones are blocked, bone becomes less dense and breaks more easily.

Bone mineral density testing can also detect osteopenia, an intermediate stage of bone loss between normal bone density and osteoporosis.

A DXA test (sometimes called a DEXA test) is considered the standard bone mineral density test because it is the most accurate and uses the least radiation. Low-dose X-rays are used to evaluate specific bones — generally the lower spine (lumbar spine) and the hip (femur).

For a DXA test you lie on a cushioned table while a scanner passes over your body. It is best to wear loose, comfortable clothing, but some centres prefer you to change into a gown. You will probably be asked to take off anything containing metal, such as jewelry or glasses. The test is painless and usually takes about 20 minutes.

Mineral density tests are interpreted by specially trained doctors called radiologists. The radiologist will send a report back to the doctor who referred you.

The radiologist will calculate 2 scores to help interpret your bone mineral density test: a T score and a Z score.

  • T score. This indicates how dense your bone is compared to what would be expected in a young healthy adult of your sex. Your T score is the number of units — standard deviations (SD) — that your bone density is above or below the young healthy average.
    The more negative the T score, the thinner your bones and the more likely they are to break easily. A T score above -1 is considered normal, between -1 and -2.5 is considered osteopenia (low bone mass) and -2.5 or a more negative score is considered osteoporosis.

t score diagram

  • Z score. This compares your bone density to that of other people your age, sex and race. Your Z score should be between -2 and +2. A Z score more negative than -2 (e.g. -2.5) could indicate that you are losing bone for a reason unrelated to age, so your doctor will probably want to do further investigations.