Clinical Laboratory - Transfusion Medicine
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Blood Components Available for Transfusion
There are a variety of blood products, pharmacologic agents, and procedures that can be utilized to treat anemia, thrombocytopenia, and bleeding disorders. Here is a brief overview of the products and services available:
Packed Red Blood Cells (PRBCs)
Packed red blood cells (PRBCs) are made from a unit of whole blood by centrifugation and removal of most of the plasma, leaving a unit with a hematocrit of about 60%. One PRBC unit will raise the hemoglobin 1 g/dl and the hematocrit of a standard adult patient by 3% (or about 1%/mL/kg in a child - 12%/25 kg with the standard 300 mL PRBC unit).
PRBCs are used to replace red cell mass when tissue oxygenation is impaired by acute or chronic anemia. PRBCs are generally indicated with a hemoglobin of 7-8 g/dl, a markedly decreased O2 saturation, and/or orthostatic hypotension. Don't transfuse more units of blood than absolutely necessary.
Infusion should proceed at the fastest rate the patient can tolerate, but less than 4 hours. The efficacy and effects of transfusion of PRBCs are monitored via physical findings and laboratory testing. Vital signs are typically logged in 15 minute intervals, and hemoglobin and hematocrit levels are determined as a part of the Complete Blood Count (CBC).
Fresh Frozen Plasma (FFP)
FFP contains all factors of the soluble coagulation system, including the labile factors V and VIII. FFP is indicated when a patient has MULTIPLE factor deficiencies and is BLEEDING, or for TTP. The PT and PTT will be prolonged, and the INR generally should be greater than 1.6. Note that FFP SHOULD NEVER be used as a plasma expander.
The efficacy of FFP can be monitored with coagulation testing.
Cryoprecipitate (cryo) contains a concentrated subset of FFP components including fibrinogen, factor VIII coagulant, vonWillebrand factor, and factor XIII. Cryoprecipitate is used for hypofibrinogenemia, von Willebrand disease, and in situations calling for a "fibrin glue." Cryo IS NOT just a concentrate of FFP. In fact, a unit of cryo contains only 40-50% of the coag factors found in a unit of FFP, but those factors are more concentrated in the cryo (less volume).
A single platelet unit is derived from one whole blood unit collected. Platelets are stored at room temperature and CANNOT be frozen. They must be used in 5 days. Pooled platelets from multiple donors from whole blood collections are cheaper to produce but the exposure to the recipient increases.
A "six pack" of platelets can be obtained by apheresis from a single donor at one time. Thus, apheresis platelets give just "one donor" exposure to the recipient, but the cost is high. The recipient's HLA type can be "matched" to a platelet donor with a similar HLA type to deal with problems of HLA alloimmunization (in patients with prior transfusions or pregnancies). The expected incremental increase in platelet count for adults is 30 - 60 K for each "six pack" of platelets.
The usage of platelets is indicated if the platelet count (in microliters) is:
- Less than 10,000 in a stable patient;
- Less than 50,000 and there is active bleeding;
- Less than 50,000 and an invasive or surgical procedures is planned;
- Less than 100,000 and a neurosurgical procedure is planned
Upon administration of platelets, the efficacy of treatment is measured by post-transfusion platelet count. If the count drops quickly, it is likely that platelets are being consumed rapidly and further transfusions of platelets may be ineffective.
Non-Blood Components Available for Transfusion
Normal saline is used when providing vascular access and fluid volume when transfusing other products and pharmacologic agents. Normal saline is more readily accessible than albumin or FFP, it is relatively inexpensive, and it does not have the risk of viral transmission.
Albumin is useful as a plasma expander. Albumin is not always readily accessible and it is expensive, but it does not have the risk of viral transmission.