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Cell washing centrifuges are used in performing blood grouping, typing, compatibility and cross-matching; Rh and antiglobulin (AGT or Coombs) tests; and slide staining. They contain the same basic components as any other centrifuge: the electric motor, the rotor or head, the bowl, and the motor drive electronics. Some cell washing centrifuges also employ the cooling system used in "regular" refrigerated centrifuges. The characteristic that distinguishes a cell washing centrifuge is the special purpose rotor or head fitted to the motor shaft. This head facilitates automatic washing, decanting, mixing, and rewashing of red blood cells. Other ancillary components facilitate the concentration of cells onto slides for microscopic evaluation.
Many of the principles outlined in this article also apply to auto-transfusion units-medical devices that connect to a patient, collect specific components of their blood, and reinfuse the remainder plus replacement fluid. At the heart of most auto-transfusion units is a cell separating and washing centrifuge. In a sense, an auto-transfusion unit is the ultimate in semi or fully automatic control of a cell washing centrifuge and its ancillary components.
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Cell washing begins as any other centrifuge operation: loading test tubes into their holders in the rotor. But unlike normal centrifugation, the caps are removed from the tubes before a lab technician places them into the rotor. Sometimes a separate cover is lowered and secured over the rotor, while other designs incorporate the cover into the lid. A typical wash cycle consists of filling the test tube with saline, centrifuging it, then removal of the supernatant. A subsequent cycle begins by resuspending the sediment in fresh saline solution, usually agitating the tubes, and then repeating the process.
Test tubes can be filled two ways: manually by the technician on basic models, or automatically through the use of a container of cell washing solution. That would normally be an IV bag of saline solution and a saline distribution manifold mounted in the cover or on the lid over the rotor on fully automatic models. Once the tubes are filled, they are generally agitated by rapid oscillating rotor movement and then centrifuged to separate the cells from the wash solution, which becomes supernatant. Once the rotor comes to a stop, the bottom of the tubes are held in...