Blood collection can vary in numerous ways, and the influence of various procedures on the peptide and protein content has been the topic of several studies. Serum has historically been used to archive patient materials, and remains the most important matrix for clinical chemistry measurements. However, the ex vivo clotting of serum might lead to neo-generation of peptides that might change the peptide composition in the specimen. For preparation of plasma samples, on the other hand, several anticoagulant can be used, and, depending on centrifugation conditions, s certain degree of platelet depletion can be established. As shown in studies of the human proteome organization (HUPO) plasma proteome project (PPP), there is a substantial contribution of platelets derived peptides to the total number of peptide (in HUPO specimen) that might be explained either by remaining platelets in the samples or by their activation before removal.