Blood is the most commonly used biofluid for EV studies, but it’s also one of the most challenging because it’s a complex, protein-dense environment. EVs are mixed with many other blood components, especially lipoproteins, immunoglobulins, platelets, and soluble proteins, that can co-purify with EVs and limit what you can confidently measure. In fact, EVs are often a minority population compared with other particles, which makes it easy to misinterpret signals if confounders aren’t considered.

A central message of the guideline is that absolute separation doesn’t exist in blood EV research. Instead, every method is an enrichment strategy with trade-offs. The draft highlights the need to choose methods based on your research question while balancing purity, yield, and heterogeneity, and being clear about what remains in the sample after isolation. It also distinguishes “enrich” (increasing EV yield/concentration) from “purify” (increasing specificity by reducing non-EV components), and notes that combining methods is often necessary for blood.

Because many common tools (like NTA, flow cytometry, and TEM) can struggle to distinguish EVs from lipoproteins or platelets, the draft emphasizes using multiple orthogonal approaches and clearly stating what each method can and cannot prove. It also calls for more transparent, detailed reporting (instrument settings, calibration, workflow parameters, and cross-validation), since limited reporting reduces rigor and reproducibility. The reporting section reinforces that not every technique fits every study, but researchers should explain their choices and provide the key context needed to interpret results.

Blood EV results can shift long before any isolation method is applied. The guideline highlights that pre-analytical factors, like delays in processing, centrifugation conditions, clotting, freeze–thaw cycles, and storage, can dramatically change EV yield and apparent composition, and may enrich or deplete specific EV subsets. For that reason, the work emphasizes documenting and controlling these steps as part of building more reproducible, clinically relevant blood EV research.