UNCERTAINTIES IN BONE-MINERAL DENSITY T-SCORES

In the diagnosis and management of osteopenia and osteoporosis, dual p hoton absorptiometric measurements of lumbar spine and proximal femur bone mineral density are interpreted by calculating a T score, which i s the number of standard deviations by which a result deviates from th e mean bane density in young adults of the same sex. Threshold values are then used to categorize patients as having osteopenia or osteoporo sis, The uncertainty associated with a single bone mineral density mea surement, as well as the uncertainties in the assumed values for the b one mineral density in young adults and the population standard deviat ion, combine to create an uncertainty in the calculated T score, It is estimated that 95% of bone density measurements have a T score uncert ainty of less than 0.4. This means that a single measurement of bone m ineral density should not be used in isolation to assign a given patie nt to a specific diagnostic category. Rather, a bone mineral density m easurement should be regarded as only one of the variables that determ ine the risk of fracture in a given patient.