Chapter 92: Transfusion of Platelets

• 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.

• 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.

• 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.

• 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 may respond to single-donor platelets from either family members or unrelated individuals selected by matching for the HLA-A and B antigens.

• Rh-negative recipients may become sensitized to Rh-positive red cells contaminating infused platelets.

• During and after platelet transfusion, chills and fever may occur from alloantibodies against contaminating leukocytes.

• Leukocyte depletion reduces the frequency of chills and fever.

• Febrile reactions may be caused by allergic reactions to some component(s) of the suspending plasma.

• Graft-versus-host disease may occur in immunosuppressed patients given unirradiated platelet transfusions.

Transmission of Microorganisms

• Chills immediately on infusion of platelets suggest bacterial contamination of the unit.

• Contamination of stored platelets by bacteria is much more common than contamination of other blood products; because they are stored at room temperature and because of their normally turbid appearance, an infected platelet unit may not appear physically different from a normal unit.

• Platelet transfusion can transmit viruses (eg, hepatitis B and C, HIV, and cytomegalovirus).

• Platelet counts of greater than 5 to 10 × 10⁹/L are adequate to protect patients against life-threatening spontaneous bleeding.

• Invasive procedures may require raising the platelet count to approximately 60 × 10⁹/L.

• ∈-Aminocaproic acid (3–5 g orally every 6 hours) can reduce mucosal bleeding in thrombocytopenic patients.

Thrombocytopenia as a Result of Underproduction

• Platelets should be transfused prophylactically for a platelet count of 5 × 10⁹/L or less, unless the patient has little hope of significant recovery from the underlying cause of thrombocytopenia, in which case bleeding should inform the decision to transfuse.

• Transfusion to maintain platelet counts greater than 20 × 10⁹/L without regard to special circumstances has no support from clinical studies and results in waste of platelets and unnecessary risks to patients.

• The decision whether to transfuse platelets in the range of 5 to 20 × 10⁹/L must be made on an individual basis using clinical considerations such as the presence of fever and sepsis, the presence of gastrointestinal ulceration or bleeding, the administration of drugs that interfere with platelet function, abnormalities of coagulation factors, and/or a very high leukocyte count.

Thrombocytopenia Caused by Platelet Loss, Sequestration, or Destruction

• Massive red blood cell transfusion only rarely requires prophylactic platelet transfusion unless there is abnormal bleeding.

• Prophylactic platelet transfusion is not indicated for the thrombocytopenia that develops after cardiopulmonary bypass unless there is abnormal bleeding.

• Thrombocytopenia from splenomegaly and sequestration of platelets does not usually require prophylactic platelet transfusion unless an invasive procedure is to be done.

• Patients with immune thrombocytopenia do not usually require platelet transfusion.

• If bleeding is life-threatening, 3 to 6 units of random-donor platelets per square meter of body surface area may raise the platelet count for 12 to 48 hours.

• The same considerations apply for other disorders with accelerated destruction of platelets, (eg, thrombotic thrombocytopenic purpura, disseminated intravascular coagulation).

• Transfusion of washed maternal platelets to an infant is indicated in neonatal alloimmune thrombocytopenia. Unfortunately, arranging for apheresis of the mother often is difficult, so transfusion of platelet concentrates to neonates who are severely thrombocytopenic or bleeding is appropriate and lifesaving. It is not appropriate to wait for the laboratory confirmation of the diagnosis in suspected cases.

Qualitative Platelet Disorders

• Platelet transfusion is not indicated for extrinsic platelet disorders (eg, uremia, von Willebrand disease, hyperglobulinemia).

• Inherited intrinsic platelet disorders are often mild and do not require platelet transfusion except for severe bleeding and surgery.

• Acquired intrinsic platelet disorders usually do not require platelet transfusion unless the patient is also thrombocytopenic.