The Z value of bone density is between 2 and (-2), and the specific meaning of Z value of bone density is the standard deviation of bone density from normal people of the same age, which reflects the value of bone density of the same age after a sample survey, and takes the form of standard deviation to reflect the number. If the Z value is lower than (-2), it means that osteoporosis is possible and the body needs normal treatment to prevent fractures. In addition, the Z-value of bone density does not respond as accurately as the T-value, so the T-value of bone density is generally used to indicate osteoporosis.