The results of bone mineral density examination need to be compared with two standards, "young people's standard" and "peer standard"
Young people's standard: judging by T score, that is, comparing the test results with the average value of healthy young people to determine the fracture risk. The lower the BMD, the higher the fracture risk.
Peer standard: judged by Z score, that is, the test results are compared with the average value of healthy people of the same age and size.
There is a standard deviation (SD) between the measurement results of BMD and the data of healthy young people. According to WHO diagnostic criteria, BMD is considered normal if the T value is within the "standard" range. Who defines osteoporosis based on bone mineral density.
Normal: Bone mineral density is within 1SD of the average value of young people (+1 ~- 1SD).
Low bone density: the bone density is lower than the average of young people (1 ~ 2.5 SD).
Osteoporosis: the bone mineral density is 2.5SD lower than the average of young people (lower than -2.5SD).
Severe osteoporosis: the bone mineral density is lower than the average level of young people by 2.5SD, accompanied by one or more osteoporotic fractures.