Blood Separation Methods: Centrifugation & Filtration Explained

Separating blood into components (plasma, serum, RBCs, WBCs, platelets) is fundamental for transfusion, diagnostics, and research.

1. Centrifugation (Standard)

• Principle: Sedimentation by centrifugal force (g-force). Denser components migrate outward.
• Standard Spin (Hard Spin): 2200–2500g × 10–15 min.
  • Bottom: Packed RBCs (hematocrit ~80%).
  • Middle: Buffy coat (WBCs + platelets) — <1% volume.
  • Top: Plasma (55% volume).
• Soft Spin (PRP Prep): 150–200g × 5–10 min.
  • Bottom: RBCs.
  • Top: Platelet-Rich Plasma (PRP) — platelets suspended in plasma.
• Double Spin (Component Therapy): Hard spin → separate plasma → second spin on plasma to concentrate platelets (platelet concentrate) or remove residual platelets (platelet-poor plasma).
• Anticoagulant Required: Citrate (CPD, ACD), heparin, EDTA — prevents clotting during spin.

2. Filtration

• Leukoreduction Filters: Remove WBCs (<5×10⁶/unit) from whole blood or components — prevents febrile reactions, HLA alloimmunization, CMV transmission. Standard for allogeneic transfusion.
• Platelet-Poor Plasma Filtration: Removes platelets from plasma.
• Membrane Plasma Separation (Plasmapheresis): Continuous flow centrifugation or hollow-fiber membrane — separates plasma from cellular components in real-time (therapeutic plasma exchange).

3. Precipitation (Fractionation)

• Cohn Process (Ethanol Fractionation): Industrial scale. Cold ethanol at varying pH/ionic strength/protein concentration precipitates specific proteins (Albumin, IgG, Factor VIII, etc.). Basis of plasma-derived medicinal products.
• Lab Scale: Ammonium sulfate, PEG precipitation for protein isolation.

4. Apheresis (Automated Cell Separation)

Continuous flow centrifugation (COBE, Spectra, Amicus) — selectively collects one component (platelets, plasma, RBCs, stem cells, granulocytes) and returns rest to donor/patient.

Clinical Products

• RBCs (packed, leukoreduced, irradiated, washed).
• Platelets (apheresis single-donor vs. pooled whole-blood derived).
• Plasma (FFP, cryoprecipitate-reduced, cryoprecipitate).
• Granulocytes, Stem cells.