Chapter 93: 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 to 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-old 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 percent 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 percent 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 (e.g., amphotericin).

Alloimmunization

• Frequently develops in patients receiving random-donor platelet transfusions.

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

• Usually caused by development of antibody against HLA antigen on the platelet surface. Leukocyte depletion of platelet products may reduce alloimmunization.

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