Chapter 92: Transfusion of Platelets

PLATELET PRODUCTS FOR TRANSFUSION

• 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.

STORAGE OF PLATELET CONCENTRATES

• 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.

CHOICE OF A PLATELET PREPARATION

• 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.

CLINICAL RESPONSE AND COMPLICATIONS OF PLATELET TRANSFUSION

• 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).

Alloimmunization

• 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 ...