Least significant change (LSC) is a precision statistic used with DXA scans. Every scanner has a small amount of measurement error even when nothing about your body has changed; the LSC is the size of difference between two scans that is large enough (at 95% confidence) to be a real change rather than that error. Facilities calculate it by scanning the same people twice and measuring the spread.
For someone tracking a GLP-1 journey, LSC is the difference between a meaningful result and a misread. A lean-mass "loss" of 300 grams between scans on a machine whose LSC for lean mass is 1 kg is not evidence of anything — it is inside the noise. Ask the facility for its LSC values, get repeat scans on the same machine, and treat changes smaller than the LSC as "no measurable change." See reading your DXA results over time.