This article will review the content indication and dosing of the major blood components, red cells, platelets, plasma, and cryoprecipitate.

INTRODUCTION:

A unit of blood divided into components can support the transfusion needs of several patients, therefore conserving blood resources.  Specific hemotherapy or the transfusion of blood components (red cells, platelets, plasma, cryoprecipitate), as opposed to whole blood, provides optimal patient care.  Although the indications for use, dosing, and expected outcome for each of the blood components should be based on the patient clinical status and not on a predetermined laboratory value.  Whenever a blood component transfusion is being planned, the use of pharmacological alternatives should also be evaluated.  All blood components must be transfused through an infusion filter (120m ).  The maximum allowable time for the transfusion is four hours.  The transfusion rate should be determined by the patient clinical status.

PACKED RED BLOOD CELLS (RBCs):

The volume, hematocrit, and storage time of RBCs will depend on the anticoagulant and preservative solution used for their preparation (Table 1).  The transfusion of RBCs is indicated for the treatment of symptomatic anemia (hemoglobin <7-8 g/dL, in the setting of acute blood loss (total blood volume loss >15%), and in patients with chronic anemia secondary to bone marrow suppression.  One unit of RBCs is expected to increase the hemoglobin level by 1 g/dL or the hematocrit by about 3% in an average size adult.  The dose recommended for the pediatric population is 10-15 mL per kilogram of bodyweight.  A patient with active bleeding and/or hypersplenism might require additional RBC transfusions to maintain or increase the hemoglobin. 

PLATELETS:

Platelets can be obtained from a unit of whole blood or collected by apheresis.  The volume, platelet content, and dose of platelets will depend on the method of collection used (Table 2).  The storage time is 5 days.  Once pooled, the storage time becomes 4 hours.  The transfusion of platelets is indicated for the treatment of bleeding or its prevention prior to an invasive procedure in patients with thrombocytopenia (platelet count <50,000/mL) or congenital or acquired platelet dysfunction.  Platelet transfusion may be indicated as bleeding prophylaxis in patients with thrombocytopenia (platelet count <10,000/mL) secondary to bone marrow suppression.  Prophylactic platelet transfusions have not been proven to be of any additional benefit in post-cardiac surgery or massive transfusion.  In the absence of life threatening bleeding, platelet transfusion may be contraindicated in idiopathic thrombocytopenic purpura, thrombotic thrombocytopenic purpura or heparin induced thrombocytopenia.  Using a formula based on the patient's weight (1 unit/10 kg), individual units of whole blood derived platelets can be pooled to create an adequate dose.  Each unit, (>5.5 x 10¹⁰) of platelets increases the platelet count by 5,000 - 10,000.  A single donor platelet contains the equivalent of 6 units of pooled platelets and this is considered an adequate dose for an average size adult.  Refractoriness to platelet transfusion may occur in conditions in which there is an increase in platelet utilization and/or consumption.  The cause of refractoriness can be clinical and/or immune.  A one hour post-platelet transfusion platelet count can distinguish between the two causes and guide the management.

Plasma

Plasma is obtained from a unit of whole blood and contains approximately 200-220 ml per bag.  It is stored frozen for up to one year.  Plasma is indicated for the treatment of bleeding or prior to an invasive procedure in patients with acquired or prevention of coagulation factor deficiencies (PT or PTT ³ 1.5 times prolongation over normal range, or INR ³ 1.6).  The use of plasma is also indicated for fluid replacement during therapeutic plasmapheresis in patients with thrombotic thrombocytopenia purpura.  Prophylactic plasma transfusion has not been proven to be of benefit after cardiac surgery or massive transfusion.  Protamine, not plasma, is indicated for the reversal of heparin-induced anticoagulation.  Thawed plasma (Table 3) can be used interchangeably with FFP, unless the clinical condition is associated with consumptive coagulopathy such as disseminated intravascular coagulation.  Plasma should be dosed at 15 ml/kg.

Cryoprecipitate

Cryoprecipitate is prepared from a unit of fresh frozen plasma.  The FFP is slowly thawed at a cold temperature triggering the precipitation of certain proteins present in the plasma followed by the removal of the supernatant.  Each unit (bag) of cryoprecipitate contains ± 80-120 units of Factor VIII:C and Factor VIII:vWF; ³ 150 mg of fibrinogen.  It is stored frozen and thawed for transfusion.  Once thawed, cryoprecipitate is stored at room temperature for four (4) hours (pooled) or six (6) hours (unpooled) after preparation.  The transfusion of cryoprecipitate is indicated for treatment of bleeding or its prevention prior to an invasive procedure in patients with hypofibrinogenemia (fibrinogen level < 100 mg/dL).   Cryoprecipitate is also used in the preparation of fibrin glue.  The fibrin glue is a topical adhesive used for certain surgical procedures which consist of a mixture of thrombin and cryoprecipitate.  The availability of specific coagulation factor concentrates for the treatment of hemophilia A or von Willebrand's Disease has limited the use of cryoprecipitate to a secondary therapeutic modality in the treatment of these diseases.  The calculation of a dose for the treatment of hypofibrinogenemia should be based on the patient's plasma volume and the desired vs the initial fibrinogen level.  A unit of cryoprecipitate increases the fibrinogen level by 5 mg in an average size adult.

REFERENCES:

1. Blood Transfusion Therapy - A physician's handbook, 6th Edition.   American Association of Blood Banks.

2. Lyons V. and Triulzi D.J.  Platelet transfusion therapy.  Transfusion Medicine Update.  September, 1999.