Protein expression units? I'm starting for protein expression analysis. 

In gene expression, we have TPM, RPKM etc. However, all I can see for protein expression is: "High", "Medium", "Low" and "Not detected".


  https://www.proteinatlas.org/ENSG00000140326-CDAN1/tissue




Q: Is there a unit for measuring protein expression like gene expression? I've seen people talking about PE (protein existence). Can we use it for protein expression?
I would guess that the real unit for measuring protein expression would be pM (pico-moles) or a count of protein molecules.

I'm not sure we have any methods to calculate such quantities though.