Blood-derived evs are more challenging to study
Blood has a plethora of elements beyond extracelluar vesicle. The biggest challenge is the separation of the lipoproteins that can overwhelm the study of vesicles (they can be 100-fold more abundant). Moreover, EVs are mostly derived from platelets, red blood cells, and leucocytes.
Most challenging still is that platelets can be activated during blood collection, handling, and storage. Release of EVs can therefore confound the results[@ramirez-garrastacho2021Extracellular vesicles as a source of prostate cancer biomarkers in liquid biopsies: a decade of research].
Again, this relates to the challenge of EV isolation and purification
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