What is a significant change in t/z scores for osteoporosis? my spine is -8.6% worse... is that a lot for 1 year? femurs change are -0.007% and -0.5%.

High variability: A significant problem with DEXA scans is the variability both between different machines and within the same center. The reported variability using the same machine on two different days is about 4%. If one tries to compare two different machines (and operators), the variability can be as high as 10-15%. It looks like your spine may be worse, but the femur is unchanged.