The present invention relates, e.g., to a method for detecting a full-length protein and a truncated form (e.g., a naturally occurring cleavage product) thereof, in a sample, comprisingoptionally denaturing and reducing proteins in the sample,cleaving the proteins into smaller peptides, anddetecting a unique peptide identifier for the full-length protein and / or a unique peptide identifier for the truncated protein, in the sample.In one embodiment of the invention, the full-length protein is thioredoxin (TRX), and the truncated form thereof is its biologically active, C-terminal truncated, 10 kDa cleavage product, TRX 80.