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Blood Products

by Ravindra Sarode, MD

Whole blood can provide improved O 2 -carrying capacity, volume expansion, and replacement of clotting factors and was previously recommended for rapid massive blood loss. However, because component therapy is equally effective and is a more efficient use of donated blood, whole blood is not generally available in the US.

RBCs

Packed RBCs are ordinarily the component of choice with which to increase Hb. Indications depend on the patient. O 2 -carrying capacity may be adequate with Hb levels as low as 7 g/L in healthy patients, but transfusion may be indicated with higher Hb levels in patients with decreased cardiopulmonary reserve or ongoing bleeding. One unit of RBCs increases an average adult’s Hb by about 1 g/dL, and the Hct by about 3% above the pretransfusion Hct value. When only volume expansion is required, other fluids can be used concurrently or separately. In patients with multiple blood group antibodies or with antibodies to high-frequency RBC antigens, rare frozen RBCs are used.

Washed RBCs are free of almost all traces of plasma, most WBCs, and platelets. They are generally given to patients who have severe reactions to plasma (eg, severe allergies, paroxysmal nocturnal hemoglobinuria, IgA immunization). In IgA-immunized patients, blood collected from IgA-deficient donors may be preferable for transfusion.

WBC-depleted RBCs are prepared with special filters that remove 99.99% of WBCs. They are indicated for patients who have experienced nonhemolytic febrile transfusion reactions, for exchange transfusions, for patients who require cytomegalovirus-negative blood that is unavailable, and possibly for the prevention of HLA alloimmunization to help prevent refractoriness to platelet transfusion (failure to achieve the target level of blood platelets after platelet transfusion).

Fresh frozen plasma

Fresh frozen plasma (FFP) is an unconcentrated source of all clotting factors without platelets. Indications include correction of bleeding secondary to factor deficiencies for which specific factor replacements are unavailable, multifactor deficiency states (eg, massive transfusion, disseminated intravascular coagulation [DIC], liver failure), and urgent warfarin reversal, although prothrombin complex concentrate (PCC) is the first choice if available. FFP can supplement RBCs when whole blood is unavailable for neonatal exchange transfusion. FFP should not be used simply for volume expansion.

Cryoprecipitate

Cryoprecipitate is a concentrate prepared from FFP. Each concentrate usually contains about 80 units each of factor VIII and von Willebrand factor and about 250 mg of fibrinogen. It also contains ADAMTS13 (an enzyme that is deficient in congenital thrombotic thrombocytopenic purpura), fibronectin, and factor XIII. Although originally used for hemophilia and von Willebrand disease, cryoprecipitate is currently used as a source of fibrinogen in acute DIC with bleeding, treatment of uremic bleeding, cardiothoracic surgery (fibrin glue), obstetric emergencies such as abruptio placentae and HELLP (hemolysis, elevated liver enzymes, and low platelet count) syndrome, and rare factor XIII deficiency when human coagulation factor XIII concentrate is unavailable. In general, it should not be used for other indications.

WBCs

Granulocytes may be transfused when sepsis occurs in a patient with profound persistent neutropenia (neutrophils < 500/μL) who is unresponsive to antibiotics (see Neutropenia). Granulocytes must be given within 24 h of harvest; however, testing for HIV, hepatitis, human T-cell lymphotropic virus, and syphilis may not be completed before infusion. Because of improved antibiotic therapy and drugs that stimulate granulocyte production during chemotherapy, granulocytes are seldom used.

Immune globulins

Rh immune globulin (RhIg), given IM or IV, prevents development of maternal Rh antibodies that can result from fetomaternal hemorrhage. The standard dose of intramuscular RhIg (300 mcg) must be given to an Rh-negative mother immediately after abortion or delivery (live or stillborn) unless the infant is Rh 0 (D) and D u negative or the mother’s serum already contains anti-Rh 0 (D). If fetomaternal hemorrhage is > 30 mL, a larger dose is needed. If hemorrhage of this amount is suspected, testing of the volume of fetomaternal hemorrhage begins with the screening rosette test, which, if positive, is followed by a quantitative test (eg, Kleihauer-Betke test). RhIg is also used to treat immune thrombocytopenia (ITP), in which case it is given IV.

Other immune globulins are available for postexposure prophylaxis for patients exposed to a number of infectious diseases, including cytomegalovirus, hepatitis A and B, measles, rabies, respiratory syncytial virus, rubella, tetanus, smallpox, and varicella (for usage, see under specific disease).

Platelets

Platelet concentrates are used

  • To prevent bleeding in asymptomatic severe thrombocytopenia (platelet count < 10,000/μL

  • For bleeding patients with less severe thrombocytopenia (platelet count < 50,000/μL)

  • For bleeding patients with platelet dysfunction due to antiplatelet drugs but with normal platelet count

  • For patients receiving massive transfusion that causes dilutional thrombocytopenia

Platelet concentrates are also sometimes used before invasive surgery, particularly with extracorporeal circulation for > 2 h (which often makes platelets dysfunctional). One platelet concentrate unit increases the platelet count by about 10,000/μL, and adequate hemostasis is achieved with a platelet count of about 10,000/μL in a patient without complicating conditions and about 50,000/μL for those undergoing surgery. Therefore, 4 to 6 units of random donor platelet concentrates are commonly used in adults.

Platelet concentrates are increasingly being prepared by automated devices that harvest the platelets (or other cells) and return unneeded components (eg, RBCs, plasma) to the donor. This procedure, called cytapheresis, provides enough platelets from a single donation (equivalent to 4 to 6 random platelet units) for transfusion to an adult, which, because it minimizes infectious and immunogenic risks, is preferred to multiple donor transfusions in certain conditions.

Certain patients may not respond to platelet transfusions (called refractoriness), possibly because of splenic sequestration, platelet consumption due to DIC, or destruction due to HLA or platelet-specific antigen alloimmunization (and immune-mediated destruction). If patients are refractory to transfusion, they are tested for alloimmunization if possible. Patients with immune-mediated destruction may respond to multiple random donor platelets (because of greater likelihood that some units are HLA compatible), platelets from family members, or ABO- or HLA-matched platelets. HLA alloimmunization may be mitigated by transfusing WBC-depleted RBCs and WBC-depleted platelet concentrates.

Other products

Irradiated blood products are used to prevent graft-vs-host disease in patients at risk (see Graft-vs-host disease (GVHD)). Many attempts have been made to develop blood substitutes using inert chemicals (eg, perfluorocarbons) or Hb solutions to carry and deliver O 2 to tissues. Although these Hb substitutes had promising ability to deliver O 2 to tissues during an emergency, several clinical trials have failed due to increased mortality and severe adverse cardiovascular toxicities (eg, hypotension). Currently, attempts to regenerate platelets and RBCs from various stem cell sources are underway.

Hematopoietic progenitor cells (stem cells) from autologous or allogenic donors can be transfused as a way of reconstituting hematopoietic function (particularly immune function) in patients undergoing myeloablative or myelotoxic therapy (see Hematopoietic Stem Cell Transplantation).

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