The T-score compares the bone density of a healthy, young adult of the same sex to the patient, according to Mayo Clinic.The Z-score is the standard deviation of what is typically expected of an adult of the same age, weight, race and sex as the patient.
A person with a T-score of -1 and above is considered to have normal bone density, explains Mayo Clinic. A score between -1 and -2.5 means that a person may have osteopenia, which may lead to osteoporosis. A score of -2.5 and lower means that the patient is likely to have osteoporosis. Bone loss in those who score -2 or lower on the Z-score may be due to something other than aging.
Most Z-scores are not typically used to diagnose osteoporosis but are used to look for potential causes of bone density loss, notes WebMD. To determine the amount of bone density loss, the T-score is multiplied by 10 percent. Women who have yet to reach menopausal age and men under the age of 50 have a low risk factor for fractures even if a T-score of -2.5 or lower has been received. Those diagnosed with osteoporosis are at risk for fractures, and treatment is recommended. Those diagnosed with osteopenia do not need to seek treatment; however, consistent monitoring is suggested.