January, 1995
PLASMA TRANSFUSION THERAPY Darrell J. Triulzi, M.D., Medical Director, Centralized Transfusion Services,
INTRODUCTION Platelets transfusions have become an integral part of the care for numerous patients with disease or treatment related thrombocytopenia. Continuing concern over the risks and costs of platelet transfusion have provided the impetus to continuously review appropriate indications for their use.
Description A random donor platelet concentrate is prepared from a single unit of whole blood and contains approximately 0.6 x 1011 platelets and 50 ml of plasma. A therapeutic dose is 1 unit/10 kg body weight pool or approximately 6-7 units in an adult. Each unit would be expected to raise the platelet count by 5,000 - 10,000/ul. A single donor platelet is obtained by apheresis and contains 3-6 x 1011 platelets in 250-450 ml plasma. Thus, a single donor platelet is equivalent to a 6-8 unit pool of random donor platelets and would constitute one therapeutic dose. Platelets may be stored for up to 5 days at room temperature. Once pooled they must be given within 4 hours to maintain sterility.
Complications of Platelet Transfusion Platelet transfusions are capable of transmitting blood borne pathogens with a risk similar to that associated with whole blood, red cells, or plasma. Since platelets are typically administered in pools of 6-8 units, the risk is increased with the increased number of donor exposures. Current estimates per tested unit for transmission of hepatitis C is >1:3,300, HIV 1:400,000, and hepatitis B 1:200,000. Platelet transfusions are also associated with other risks including fever-chill non-hemolytic transfusion reactions and allergic transfusion reactions. These can occur in as many as 30% of platelet transfusion episodes. Lastly, white cells contaminating platelet products may induce HLA antibodies in the recipient; a process called alloimmunization. HLA antibodies in the patient may bind to transfused platelets resulting in poor platelet increments (refractoriness). The risk of alloimmunization is 50% in patients receiving multiple platelet transfusions. This can be reduced to 20% by removing the white cells from the product prior to transfusion (leukodepletion). Limiting the number of platelet transfusions may reduce the risk of these complications. Indications For Platelets In The Non-bleeding Patient The prophylactic use of platelets in severely thrombocytopenic patients has been well entrenched in transfusion practice. Traditionally a platelet trigger of 20,000/ul has been used. This number is based on a 1962 study of leukemia patients concomitantly treated with aspirin. Several recent studies have questioned the validity of this trigger and have shown that patients without other risk factors for bleeding can be safely observed until the platelet count drops to 10,000/ul or even less. Patients with risk factors for bleeding including: infections, coagulopathy, heparin therapy, splenomegaly, or sepsis may require higher thresholds. It is controversial whether fever without other evidence of infection warrants use of a higher threshold.
Indications for Platelets in Bleeding Patients or Patients Undergoing Invasive Procedures Platelet transfusion are indicated in patients with active bleeding and platelet counts <50,000/ul. Minor bleeding confined to the skin (petechiae, ecchymosis) generally does not require platelet transfusion to this level. Platelet transfusions are also indicted in patients who will undergo invasive procedures with platelet counts <50,000/ul. Patients with a coagulopathy or bleeding in a critical site (i.e., CNS, lungs) may require transfusion at higher levels.
Indications for Platelets in Patients with Platelet Dysfunction The utility of platelets in this setting depends on the etiology of platelet dysfunction and is independent of platelet count. Platelet transfusions may be beneficial in bleeding patients post-cardiac bypass, with aortic/ventricular assist devices, or on extracorporeal membrane oxoygenators. Patients with a recent history of aspirin use may benefit from platelet transfusion if they are bleeding or will undergo an invasive procedure. Platelet transfusions are generally not indicated in patients with platelet dysfunction due to uremia or von Willebrand's disease. Patients with immune thrombocytopenic purpura or thrombotic thrombocytopenic purpura should not be treated with platelet transfusions unless bleeding is life threatening.
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