BLOOD COMPONENTS
Blood from donors is collected as whole blood in a suitable anticoagulant. Now-a-days it is a common practice to divide whole blood in to components which include: packed RBCs, platelets, fresh-frozen plasma (FFP) and cryoprecipitate.
The procedure consists of initial centrifugation at low speed to separate whole blood into two parts: packed RBCs and platelet-rich plasma (PRP). Subsequently, PRP is centrifuged at high speed to yield two parts: random donor platelets and FFP. Cryoprecipitates are obtained by thawing of FFP followed by centrifugation. Apheresis is the technique of direct collection of large excess of platelets from a single donor.
The applications of these blood components in clinical use is briefly given below.
1. Packed RBCs.
These are used to raise the oxygen carrying capacity of blood and are used in normo volaemic patients of anaemia without cardiac disease. One unit of packed RBCs may raise haemoglobin by 1 g/dl.
2. Platelets.
Transfusion of platelets is done in patients of thrombocytopenia who have haemorrhage. Optimally, platelet transfusions can be given to a patient with platelet count below 10,000/ul. Each unit of platelets can raise platelet count by 5,000 to 10,000/μl.
3. Fresh frozen plasma.
FFP contains plasma proteins and coagulation factors that includes albumin, protein C and S and antithrombin. FFP transfusion in indicated in patients of coagulation failure and TTP. Each unit of FFP raises coagulation factors by about 2%.
4. Cryoprecipitate.
Cryoprecipitate is a source of insoluble plasma proteins, fibrinogen, factor VIII and vWF. Indications for transfusion of cryoprecipitate are for patients requiring fibrinogen, factor VIII and vWF. Transfusion of single unit of cryoprecipitate yields about 80 IU of factor VIII.