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Apheresis
Apheresis (ἀφαίρεσις (aphairesis, "a taking away")) is a medical technology in which the blood of a person is passed through an apparatus that separates one particular constituent and returns the remainder to the circulation. It is thus an extracorporeal therapy.
One of the uses of apheresis is for collecting hematopoietic stem cells.
Depending on the substance that is being removed, different processes are employed in apheresis. If separation by density is required, centrifugation is the most common method. Other methods involve absorption onto beads coated with an absorbent material and filtration.
The centrifugation method can be divided into two basic categories:
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.[citation needed]
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.
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 (lymphocytes, granulocytes, monocytes) in the middle and the plasma on top.
There are numerous types of apheresis.
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Apheresis
Apheresis (ἀφαίρεσις (aphairesis, "a taking away")) is a medical technology in which the blood of a person is passed through an apparatus that separates one particular constituent and returns the remainder to the circulation. It is thus an extracorporeal therapy.
One of the uses of apheresis is for collecting hematopoietic stem cells.
Depending on the substance that is being removed, different processes are employed in apheresis. If separation by density is required, centrifugation is the most common method. Other methods involve absorption onto beads coated with an absorbent material and filtration.
The centrifugation method can be divided into two basic categories:
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.[citation needed]
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.
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 (lymphocytes, granulocytes, monocytes) in the middle and the plasma on top.
There are numerous types of apheresis.