The Z-score for bone density is the comparison to the "age-matched normal" and is usually used in cases of severe osteoporosis. This is the standard score or number of standard deviations a patient's bone mineral density differs from the average for their age, sex, and ethnicity. This value is used in premenopausal women, men under the age of 50, and in children and adolescents. It is most useful when the score is less than 2 standard deviations below this normal. In this setting, it is helpful to scrutinize for coexisting illnesses or treatments that may contribute to osteoporosis such as glucocorticoid therapy, hyperparathyroidism, or alcoholism.
