During a bone density test, the patient lies on a platform while a type of X-ray arm passes over her body, according to Mayo Clinic. The test takes from 10 minutes to a half hour. Peripheral devices test the bone density of the extremities.
A patient takes a bone density test when her doctor suspects that her bones are likely to break because of osteoporosis, says Mayo Clinic. The bone density test focuses on the neck of the femur, the forearm bones, and the lumbar vertebrae, which are in the lower back.
After the test, the patient receives a T-score and a Z-score, according to Mayo Clinic. The T-score is the bone density compared with the bone density of a young person of the patient's sex. It is the number of standard deviations above or below average. If it is -1 and above, the patient's bone density is normal. If it's between -1 and - 2.5, her bone density is below normal. This is a condition called osteopenia. If the T-score is - 2.5 and below, it probably means the patient has osteoporosis.
The Z-score charts the standard deviations from normal for a person of the patient's sex, age, weight and ethnic or racial background, claims Mayo Clinic. A Z-score of -2 or lower indicates a problematic bone loss.