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PLATELET PRODUCTS FOR TRANSFUSION

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  • Random donor platelets are prepared by centrifugation techniques that yield from 7 to 10 × 1010 platelets per unit of blood.

  • Platelets so obtained are suspended in citrated autologous plasma and are significantly contaminated with leukocytes. Several units of platelets are pooled to provide sufficient platelets for transfusion (4–6 U for an adult).

  • Single-donor platelets are prepared from a single individual by plateletpheresis. Each plateletpheresis contains approximately 3 to 4 × 1011 platelets, significantly contaminated with leukocytes.

  • Fresh whole blood is used for platelet transfusion in children younger than 2 years of age who have undergone open heart surgery.

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STORAGE OF PLATELET CONCENTRATES

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  • Platelet suspensions may be stored with continuous agitation for 5 days at 20°C to 24°C in plastic containers, which allow for adequate diffusion of oxygen.

  • In vivo function of stored platelets is nearly normal.

  • Platelets may be stored frozen in plasma containing dimethyl sulfoxide (DMSO).

  • Viability of thawed platelets is 50% that of fresh platelets.

  • Frozen storage is usually used to provide autologous platelets for use in patients who are refractory to allogeneic platelet transfusions.

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CHOICE OF A PLATELET PREPARATION

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  • Platelet transfusion may begin with random-donor pooled platelets. However, single-donor platelets are a better product with less risk of transmission of infectious agents. As such, whole blood–derived platelet use has fallen to 15% to 20% of the platelet doses transfused in the United States because of blood center convenience (no need to separate from whole blood) and the superiority of single donor platelets.

  • ABO-compatible platelets should be used whenever possible.

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CLINICAL RESPONSE AND COMPLICATIONS OF PLATELET TRANSFUSION

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  • The response to infusion of random donor platelets can be evaluated by calculating the corrected count increment (P):

    p = C × S/U (platelets/L)

    Where C = measured platelet increase (platelets/L)

    S = body surface area in square meters

    U = number of units of platelet given

  • Average corrected count increment is 10 × 109/L.

  • In a single-donor plateletpheresis product, there are about the same number of platelets as in five random-donor units.

  • The 20-hour increment is two-thirds of the 1-hour increment under normal conditions (absence of alloimmunization, ongoing hyperconsumption of disseminated intravascular coagulation or bleeding, or pooling in an enlarged spleen).

  • Additional factors that lower the corrected count increment are loss of platelet viability in storage, stem cell transplantation, or drug therapies (eg, amphotericin).

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Alloimmunization

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  • Alloimmunization frequently develops in patients receiving random-donor platelet transfusions.

  • It should be considered if two to three consecutive random donor transfusions produce a corrected count increment of less than 3 × 109/L.

  • It is usually caused by development of antibody against human leukocyte antigen (HLA) antigen on the platelet surface. Leukocyte depletion of platelet products may reduce alloimmunization.

  • Patients may respond to single-donor platelets ...

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