Bone density

In medicine, bone density, also called bone mineral density (BMD), is the "amount of mineral per square centimeter of bone. This is the definition used in clinical practice. Actual bone density would be expressed in grams per milliliter. It is most frequently measured by x-ray absorptiometry (DXA scan) or x-ray computed tomography. Bone density is an important predictor for osteoporosis."

Measurement of bone density

Densitometry results are generally scored by two measures, the T-score and the Z-score. Scores indicate the amount one's bone mineral density varies from the mean. Negative scores indicate lower bone density, and positive scores indicate higher.

T-score

The T-score is a comparison of a patient's bone density to that of a healthy thirty-year-old. The criteria of the World Health Organization are:

• Osteoporosis is defined as -2.5 or lower, meaning a bone density that is two and a half standard deviations below the mean of a thirty year old woman.
• Osteopenia is defined as less than -1.0 and greater than -2.5
• Normal is a T-score of -1.0 or higher

Z-score

The Z-score is a comparison of a patient's BMD to the average BMD of their, sex, and race. This value is used in premenopausal women, men under aged 50, and in children.