Osteoporosis testing relies on clinical presentation, bone mass measurement (BMD), X-rays and biochemical indicators of bone conversion. Bone densitometry automatically calculates T-value and Z-value data based on patient data. t-value is the number of standard deviations (SD) that are higher (+) or lower (-) than the BMD of a young person when comparing the bone mineral density (BMD) obtained from the test with the BMD of a normal young population and is the most meaningful value for diagnosing osteoporosis. z-value is the value obtained when comparing the BMD measured from the test with the BMD of a normal young population of the same age. Although Z-values are not very meaningful for the diagnosis of osteoporosis, they can reflect the severity of osteoporosis. The World Health Organization (WHO) has determined the following four indicators based on the standard deviation (SD) between the measurement of bone mineral density (BMD) levels and the data of healthy young people. 1, normal: BMD within 1SD of the average value of young people (+1 to -1SD) 2, low BMD: BMD below the average value of young people 1 to 2.5SD (-1 to -2.5SD) 3, osteoporosis: BMD below the average value of young people 2.5SD (below -2.5SD) 4, severe osteoporosis: BMD below the average value of young people 2.5SD, with one or multiple osteoporotic fractures.