<Tr> <Td> Osteopenia </Td> <Td> 11.4 </Td> <Td> 19.6 </Td> <Td> 15.7 </Td> </Tr> <Tr> <Td> Osteoporosis </Td> <Td> 22.4 </Td> <Td> 46.6 </Td> <Td> 40.6 </Td> </Tr> <P> The Z - score is the comparison to the age - matched normal and is usually used in cases of severe osteoporosis . This is the number of standard deviations a patient's BMD differs from the average BMD of their age, sex, and ethnicity . This value is used in premenopausal women, men under the age of 50, and in children . 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 . </P> <P> Use of BMD has several limitations . </P>

What is a z score for bone density
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