Method
Depending on the substance that is being removed, different processes are employed in apheresis. If separation byContinuous flow centrifugation
Continuous flow centrifugation (CFC) historically required two venipunctures , as "continuous" means the blood is collected, spun, and returned simultaneously. Newer systems can operate with a single venipuncture by collecting blood in a vessel and alternating between drawing and returning it through the same needle, while the centrifuge continuously processes the blood held in the vessel. 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.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 a result, it is less commonly used for therapeutic purposes and is more frequently found in Donation Center settings. To stop the blood from coagulating, an anticoagulant is automatically mixed with the blood as it is pumped from the body into the apheresis machine.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 the centrifuge, the third is solutes added, and the fourth is not as easily controllable: plasma volume and cellular content of the donor. The result in most cases is the classic sedimented blood sample with the RBCs at the bottom, the buffy coat of platelets and WBCs (Types
There are numerous types of apheresis.Donation
Blood taken from a healthy donor can be separated into its parts during blood donation, where the needed component is collected and the unharvested components are returned to the donor.Donor safety
* Single use kits – Apheresis is done using single-use kits, so there is no risk of infection from blood-contaminated tubing or centrifuge. Blood does not contact the device and during the separation, blood does not exit the kit. * Reinfusion – At the end of the procedure, the remaining blood in the kit is given back to the donor with a process called 'reinfusion'. * Immune system effects – "the immediate decreases in blood lymphocyte counts and serum immunoglobulin concentrations are of slight to moderate degree and are without known adverse effects. Less information is available regarding long-term alterations of the immune system".= Kit problems
= Two apheresis kit recalls were: * Baxter Healthcare Corporation (2005), in which "pinhole leaks were observed at the two-omega end of the umbilicus (multilumen tubing), causing a blood leak." * Fenwal Incorporated (2007), in which there were "two instances where the anticoagulant citrate dextrose (ACD) and saline lines were reversed in the assembly process. The reversed line connections may not be visually apparent in the monitor box, and could result in excessive ACD infusion and severe injury, including death, to the donor."= Donor selection
= People who do not use a drug that may prevent blood donation, who do not have the risk of the carrier of a disease, and who have suitable vascular structure may be apheresis donors. For apheresis platelet donation the donor's pre platelet count should be above 150 x 10^9/L. For apheresis plasma donation, the donor's total protein level should be greater than 60 g/L. For double red cell apheresis, donors of either gender require a minimum hemoglobin level of 14.0 g/dl.= Plasticizer exposure
= Apheresis uses plastics and tubing, which come into contact with the blood. The plastics are made of PVC in addition to additives such as a plasticizer, often DEHP. DEHP leaches from the plastic into the blood, and people have begun to study the possible effects of this leached DEHP on donors as well as transfusion recipients. * "current risk or preventive limit values for DEHP such as the RfD of the US EPA (20 μg/kg/day) and the TDI of the European Union (20–48 μg/kg/day) can be exceeded on the day of the plateletpheresis. ... Especially women in their reproductive age need to be protected from DEHP exposures exceeding the above mentioned preventive limit values." * "Commercial plateletpheresis disposables release considerable amounts of DEHP during the apheresis procedure, but the total dose of DEHP retained by the donor is within the normal range of DEHP exposure of the general population." * The Baxter company manufactured blood bags without DEHP, but there was little demand for the product in the marketplace * "Mean DEHP doses for both plateletpheresis techniques (18.1 and 32.3 μg/kg/day) were close to or exceeded the reference dose (RfD) of the US EPA and tolerable daily intake (TDI) value of the EU on the day of the apheresis. Therefore, margins of safety might be insufficient to protect especially young men and women in their reproductive age from effects on reproductivity. At present, discontinuous-flow devices should be preferred to avert conceivable health risks from plateletpheresis donors. Strategies to avoid DEHP exposure of donors during apheresis need to be developed."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. For autoimmune diseases in which apheresis is effective, it is used not as a standalone treatment, but rather in conjunction with therapies that reduce production of autoantibodies. * 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 * Photopheresis – used to treatIndications
ASFA categories
In 2023, the American Society for Apheresis published the 9th Special Edition 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: * 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.Fluid replacement during apheresis
When an apheresis system is used for therapy, the system is removing relatively small amounts of fluid (not more than 10.5 mL/kg body weight). That fluid must be replaced to keep correct intravascular volume. The fluid replaced is different at different institutions. If a crystalloid like normal saline (NS) is used, the infusion amount should be triple what is removed as the 3:1 ratio of normal saline for plasma is needed to keep up oncotic pressure. Some institutions use human serum albumin, but it is costly and can be difficult to find. Routine use of fresh frozen plasma (FFP) is not generally appropriate because of the dangers including citrate toxicity (from the anticoagulant), ABO incompatibility,See also
* Leukoreduction * Plasmapheresis *References
External links
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