What is apheresis?

What is Apheresis

Apheresis is an extracorporeal blood processing procedure in which blood is withdrawn from a patient or donor, separated into its individual components using centrifugation or membrane filtration, with selective removal or collection of a specific component (plasma, platelets, white blood cells, or red blood cells), followed by return of the remaining blood components to the circulation. 1

Core Mechanism

The fundamental process involves three key steps 2, 3:

• Blood withdrawal through vascular access (typically two venipunctures—one for withdrawal, one for return)
• Component separation using either differential centrifugation or membrane filtration techniques
• Selective removal or collection of the target component with reinfusion of remaining blood elements

Primary Separation Methods

Apheresis employs three elementary physical separation techniques 4:

• Differential centrifugation: Blood passes through a blood-cell separator centrifugation system that exploits differences in density and size between blood components 1
• Membrane filtration: Sequential filtration through membranes of different pore sizes (cascade filtration), predominantly used in Europe and Japan 3
• Adsorption: Selective binding of specific proteins or cells from whole blood or pre-separated plasma 4

Major Types of Apheresis

Therapeutic Apheresis

Designed to treat diseases by removing abnormal blood cells or toxic plasma substances 4, 2:

• Plasmapheresis (plasma exchange): Removal of plasma containing pathologic substances (antibodies, immune complexes, paraproteins, cryoglobulins) 3
• Cytapheresis: Removal of excessive or abnormal cellular components
  • Leukapheresis: White blood cell removal, commonly initiated when WBC >100,000/μL or with leukostasis symptoms 3
  • Plateletpheresis: Platelet removal for symptomatic thrombocytosis 3
  • Erythrocytapheresis: Red blood cell removal for polycythemia vera or sickle cell disease 3

Productive Apheresis

Collection of blood components for transfusion purposes 4:

• Plateletpheresis for donation: Processing 4,000-5,000 mL of donor blood over 1.5-2 hours to collect platelets equivalent to 6-9 units of whole blood-derived platelets 1
• Products contain at least 3×10¹¹ platelets and are stored for up to 5 days at 20-24°C 1
• Most products now contain <5×10⁶ leukocytes (leukocyte-reduced) 1

Clinical Applications

Apheresis serves as primary or adjunctive therapy for 2:

• Hematologic disorders: Hyperviscosity syndromes (Waldenström's macroglobulinemia, multiple myeloma), hyperleukocytosis, polycythemia vera, essential thrombocytosis 3
• Neurologic conditions: Various autoimmune neurologic disorders requiring plasma exchange 2
• Renal diseases: Specific glomerulonephritides and related conditions 2
• Autoimmune/rheumatologic disorders: Conditions responsive to plasma component removal 2

Important Procedural Considerations

Single-donor apheresis platelets minimize donor exposures compared to pooled random-donor products, theoretically reducing transfusion-transmitted disease risk, though contemporary screening has made this difference clinically insignificant in patients requiring multiple transfusions 1. When leukoreduced products are available, whole blood-derived platelets perform equivalently to apheresis platelets with no significant difference in transfusion-related adverse events 1.

The procedure requires approximately 1.5-2 hours for platelet collection 1, and adverse events occur relatively frequently during apheresis procedures, necessitating careful monitoring 5.