I was trying to think of these. If I had to guess what they are based on everything I've heard:
1. electrical impedance measurements of mecfs cells exposed to salt stress. [edit: aka the nanoneedle experiment]
2. a stratification thing where mecfs cells are lighter (?) [edit, the thing
@Gemini is mentioning in the post above]
3. red blood cell shape differences
4. naviaux's metabolic panel (expensive though)
Open to disagreements / other suggestions here.