Continuous flow centrifugation

Continuous flow centrifugation (CFC) historically required two venipunctures as "continuous" means the blood is collected, spun, and returned simultaneously. Newer systems can use a single venipuncture by pooling blood in a vessel and cycling through drawing and returning blood though the needle while the centrifuge continuously processes blood remaining in the vessel.^[2] The main advantage of this system is the low extracorporeal volume (calculated by volume of the apheresis chamber, the donor's hematocrit, and total blood volume of the donor) used in the procedure, which may be advantageous in the elderly and for children.^{[citation needed]}

Intermittent flow centrifugation

Intermittent flow centrifugation (IFC) works in cycles, taking blood, spinning/processing it and then giving back the unused parts to the donor in a bolus. The main advantage is a single venipuncture site. It does require a larger extracorporeal volume, and takes significantly longer to perform the procedure via IFC. As such, it is less likely to be used for therapeutic reasons, and is often seen in Donation Center settings.^[3] To stop the blood from coagulating, anticoagulant is automatically mixed with the blood as it is pumped from the body into the apheresis machine.^{[citation needed]}

Centrifugation variables

The centrifugation process itself has four variables that can be controlled to selectively remove desired components. The first is spin speed and bowl diameter, the second is "sit time" in centrifuge, the third is solutes added, and the fourth is not as easily controllable: plasma volume and cellular content of the donor. The end product in most cases is the classic sedimented blood sample with the RBCs at the bottom, the buffy coat of platelets and WBCs (lymphocytes/granulocytes, PMNs, basophils, eosinophils/monocytes) in the middle and the plasma on top.^{[citation needed]}

Donation

Blood taken from a healthy donor can be separated into its component parts during blood donation, where the needed component is collected and the unharvested components are returned to the donor. Fluid replacement is usually not needed in this type of collection. In many countries, apheresis donors can donate blood more often than those donating whole blood. ^{[citation needed]}There are several categories of component collections:

• Plasmapheresis – blood plasma. Plasmapheresis is useful in collecting FFP (fresh frozen plasma) of a particular ABO group. Commercial uses aside from FFP for this procedure include immunoglobulin products, plasma derivatives, and collection of rare WBC and RBC antibodies.

• Erythrocytapheresis – red blood cells. Erythrocytapheresis is the separation of erythrocytes from whole blood. It is most commonly accomplished using the method of centrifugal sedimentation. This process is used for red blood cell diseases such as sickle cell crises or severe malaria. The automated red blood cell collection procedure for donating erythrocytes is referred to as 'Double Reds' or 'Double Red Cell Apheresis.'^[4]
• Plateletpheresis (thrombapheresis, thrombocytapheresis) – blood platelets. Plateletpheresis is the collection of platelets by apheresis while returning the RBCs, WBCs, and component plasma. The yield is normally the equivalent of between six and ten random platelet concentrates. Quality control demands the platelets from apheresis be equal to or greater than 3.0 × 10¹¹ in number and have a pH of equal to or greater than 6.2 in 90% of the products tested and must be used within five days.
• Leukapheresis – leukocytes (white blood cells). Leukopheresis is the removal of PMNs, basophils, eosinophils for transfusion into patients whose PMNs are ineffective or where traditional therapy has failed. There is limited data to suggest the benefit of granulocyte transfusion. The complications of this procedure are the difficulty in collection and short shelf life (24 hours at 20 to 24 °C). Since the "buffy coat" layer sits directly atop the RBC layer, HES, a sedimenting agent, is employed to improve yield while minimizing RBC collection. Quality control demands the resultant concentrate be 1.0 × 10¹⁰ granulocytes in 75% of the units tested and that the product be irradiated to avoid graft-versus-host disease (inactivate lymphocytes). Irradiation does not affect PMN function. Since there is usually a small amount of RBCs collected, ABO compatibility should be employed when feasible.^{[citation needed]}
• Stem cell harvesting – circulating bone marrow cells are harvested to use in bone marrow transplantation.^{[citation needed]}

Therapy

The various apheresis techniques may be used whenever the removed constituent is causing severe symptoms of disease. Generally, apheresis has to be performed fairly often, and is an invasive process. It is therefore only employed if other means to control a particular disease have failed, or the symptoms are of such a nature that waiting for medication to become effective would cause suffering or risk of complications.^{[citation needed]}

• Plasma exchange – removal of the liquid portion of blood to remove harmful substances. The plasma is replaced with a replacement solution.
• LDL apheresis – removal of low density lipoprotein in patients with familial hypercholesterolemia.
• Lipoprotein(a) (Lp(a) apheresis^[12]
• Photopheresis – used to treat graft-versus-host disease, cutaneous T-cell lymphoma, and rejection in heart transplantation.
• Immunoadsorbtion with Staphylococcal protein A-agarose column – removal of allo- and autoantibodies (in autoimmune diseases, transplant rejection, hemophilia) by directing plasma through protein A-agarose columns. Protein A is a cell wall component produced by several strains of Staphylococcus aureus which binds to the Fc region of IgG.
• Leukocytapheresis – removal of malignant white blood cells in people with leukemia and very high white blood cell counts causing symptoms.
• Erythrocytapheresis – removal of erythrocytes (red blood cells) in people with iron overload as a result of Hereditary haemochromatosis or transfusional iron overload
• Thrombocytapheresis – removal of platelets in people with symptoms from extreme elevations in platelet count such as those with essential thrombocythemia or polycythemia vera.

ASFA categories

In 2010, the American Society for Apheresis published the 5th Special Edition(1)^[13] of evidence based guidelines for the practice of Apheresis Medicine. These guidelines are based upon a systematic review of available scientific literature. Clinical utility for a given disease is denoted by assignment of an ASFA Category (I – IV). The quality and strength of evidence are denoted by standard GRADE recommendations. ASFA Categories are defined as follows:^{[citation needed]}

• Category I for disorders where therapeutic apheresis is accepted as a first line treatment,
• Category II for disorders where therapeutic apheresis is accepted as a second-line treatment,
• Category III for disorders where the optimal role of therapeutic apheresis is not clearly established and
• Category IV for disorders where therapeutic apheresis is considered ineffective or harmful.

Diseases and disorders

Only diseases (or mentioned special conditions thereof) with ASFA category I or II are displayed in bold, with category I being underlined in addition.