When looking at two Dexa scan results from one year to another year, the bone mineral density BMD (in grams/cm squared) changes should be compared, not the T scores. The reason is that T score is derived from one’s BMD compared to the average peak BMD and standard deviation of a population. A Dexa machine’s database could change during software updates which may render T or Z score unreliable. However BMD is the original data which the machine reads. What’s important, is to know is the LSC )least significant change) of a machine.

A Dexa report should provide all the information such as bmd% change and LSC (might be in footnote).