Platelet Concentrates

Platelets for transfusion can be prepared either by separation of platelet concentrates from whole blood or by apheresis from single donors. Comparative studies have shown that post-transfusion increment, platelet survival and hemostatic effect are similar with either product.

Random Donor Platelets

Platelets prepared from whole blood are often referred to as random donor platelet concentrates. Platelet rich plasma is separated from red blood cells by centrifugation at a low G force within 4 hours after donation. Platelet rich plasma is then centrifuged at higher G force and most of the platelet poor plasma supernatant is removed. The remaining platelet concentrate contains between 5.5 and 8.5 X 1010 platelets suspended in about 50 mL of plasma. This is approximately 70% of the platelets in the original unit of whole blood.

Platelets are stored at room temperature using continuous gentle horizontal agitation in plastic bags designed to optimize oxygen and carbon dioxide exchange. Platelets can be preserved for 5 days under these conditions. Platelet concentrates are pooled immediately prior to transfusion and can then be stored for 4 hours.

One drawback of random donor platelets is that the concentrates contain 108 to 109 white blood cells or approximately 50% of the leukocytes from the original unit of whole blood. Random donor platelets should be transfused through a bedside leukocyte reduction filter.

Random donor platelet concentrates may contain up to 0.5 mL of red cells. Transfusion of as little as 0.03 mL of RBCs can stimulate anti-D synthesis. Different studies have demonstrated that 8 to 19% of Rh negative cancer patients form anti-D antibody if transfused with Rh positive platelet concentrates. Rh negative units should be used for Rh negative female children and women of childbearing age. If this is not possible then one vial of Rh immune globulin may be given before or immediately after transfusion with Rh positive platelets. Because these patients are thrombocytopenic, it is preferable to administer anti-D intravenously. A dose of 25 ug (125 IU) will protect against 1 mL of RBCs.

Single Donor Platelets

Apheresis platelets are usually called single donor platelets because they are collected from a single donor with an automated cell separator. Donors usually have an IV line in each arm. Blood pumped from one arm passes through a blood cell separator centrifugation system that collects platelets and returns plasma and red cells to the donor’s other arm. Between 4000 and 5000 mL of blood are processed over 1.5 to 2 hours. A single donor platelet concentrate contains a minimum of 3.0 X 1011 platelets suspended in approximately 200 mL of plasma, which is the equivalent of 6 to 8 random donor platelet concentrates. They can be stored up to 5 days under the same conditions as random donor platelet concentrates. Five day old apheresis platelets produce the same posttransfusion platelet increment as one day old units.

Single donor apheresis platelets contain fewer than 5 x 106 white blood cells and are considered to be leukocyte reduced. Additional leukocyte reduction filtration is not necessary. Rh negative patients do not need Rh immune globulin after transfusion of Rh positive apheresis platelets because they contain so few red blood cells (0.001 – 0.007 mL).

Single donor platelets offer several advantages over random donor concentrates including:

  • Less inventory and pooling
  • Fewer donor exposures & fewer lookback investigations
  • Leukocyte reduction during collection eliminates the need for bedside filtration
  • Ten fold lower risk of bacterial contamination & 5 fold lower risk of septic transfusion reaction
  • Easier platelet crossmatching or HLA matching for refractory patients
  • Fewer contaminating red blood cells eliminating need for RhIg

Apheresis platelets have a higher processing fee than random donor platelets, but the cost difference is negligible when pooling and leukocyte reduction filter costs are considered.

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