Blood and blood products are collected as whole blood from donors in various anticoagulants. The blood and blood products which are used for transfusion are whole blood, packed red blood cells (PRBCs), platelet concentrates, fresh frozen plasma (FFP), cryoprecipitate, and plasma derivatives. Plasma derivatives are also used for transfusion such as albumin, intravenous immunoglobulin, anti-thrombin, and coagulation factor concentrates. Plasma derivatives are generally collected from several donors and pooled together and infectious organisms are removed by treating.

Separation of blood components from whole blood:

Blood is collected as whole blood of 450 ml (one unit of blood) in various anticoagulants. The whole blood is then processed to produce blood various blood components mentioned above. Most commonly blood is transfused as whole blood. To get blood components, whole blood is first separated by slow centrifugation into PRBCs and platelet rich/concentrated plasma. The platelet concentrated (rich) plasma is again centrifuged at high speed to produce a unit of platelet (known as random donor platelets) and FFP (fresh frozen plasma) each. Cryoprecipitate is produced by thawing FFP, which precipitate plasma proteins, which are then separated by centrifugation.

Platelets (multiple units) collected by apheresis technique from single donor is better then pooled random donor platelets, as pooled random donor platelets can contain more number of white blood cells (WBC).

Whole Blood:

Transfusion of whole blood is ideal in patients who sustained acute blood loss (from any cause such as road traffic accident, elective surgery etc.) of 25% or more of total blood volume as it can provide increased oxygen carrying capacity as well as increase in blood volume in the recipient. Whole blood is stored at 4°C as at this temperature red blood cells remain viable, but at 4°C platelets dysfunction and also degradation of some coagulation factors occur. Even in red cells on prolonged storage at 4°C affinity to oxygen increases and delivery of oxygen to tissues may hamper due to fall in 2, 3-bisphosphoglycerate levels in RBCs over time.

In most of the developed countries whole blood is not easily available, because whole blood is separated into blood components routinely, but in developing countries whole blood transfusion is still very common as facility for separating whole blood into blood components is not easily available.

Packed Red Blood Cells:

Packed red blood cells (PRBCs) are mainly used to increase oxygen carrying capacity, especially in anemic patients. Packed red blood cells are preferred over whole blood in case of anemia. Whole blood can cause fluid overload (as in general anemia patients are normovolemic) and the increase in hemoglobin level is less then that of packed red blood cells.

At hemoglobin level of 7 g/dl (7 gram/100 ml) oxygenation can be adequately maintained, but in certain medical condition the hemoglobin level need to be much higher. Transfusion of packed red blood cells should be guided by clinical picture and not by laboratory findings alone, which can have some negative impact on health of anemia patient.

Packed red blood cells should be modified to reduce/prevent certain problems such as transmission of infection, transfusion related fever and alloimmunization. Reduction of WBCs before storing (instead of bedside reduction) should be done as stored cytokine production is minimal in stored products. Plasma should be removed from PRBCs and also from other cellular components of blood such as platelets.

Platelets:

Platelet concentrate is transfused in case of thrombocytopenia (below normal platelet count) due to high risk of bleeding to reduce bleeding. Preventive or prophylactic platelet concentrate transfusion is done if platelet count is less than 10,000/microliter of blood and for doing invasive procedures the platelet count should be at least 50,000/microliter of blood.

Platelets are collected from several (5-8 donors) random donors (RD) or from a single SDAP (single-donor apheresis platelets). Commonly 1 unit of random donors (RD) platelets is transfused per 10 kg body weight and 1 unit of platelet concentrate increase platelet count by 5000-10,000/microliter. If repeated or multiple platelet transfusion is necessary, the patient should receive SDAP (single-donor apheresis platelets) and WBC reduced platelets, as the post transfusion count of platelets will not increase (due to antibodies directed against class I HLA antigens) if platelet transfusion is done using random donors (RD) platelets.

Refractoriness of platelet transfusion can be evaluated by using a corrected count increment (CCI). CCI can be calculated by the following formula:-

BSA (Body surface area in square meters)

CCI should be 10x109 and 7.5x109 after 1 hour and 18-24 hours after platelet transfusion (calculated by platelet count after 1 hour and 18-24 hours after platelet transfusion). Patients who have CCI below the above mentioned number are most likely due to multiple transfusion or due to antibodies directed against class I HLA antigens. To prevent this problem platelet cross matching should be done whenever the facility is available. CCI can also be lower if patient is suffering from fever, bleeding, splenomegaly, DIC, or medications in the recipient.

Fresh Frozen Plasma:

Fresh frozen plasma (FFP) is obtained after separating cellular components such as RBCs, platelets, WBCs and contain coagulation factors and plasma proteins such as albumins, globulins, fibrinogen, antithrombin, protein C, protein S etc.

Transfusion of fresh frozen plasma is indicated in disorders of coagulation, warfarin (an oral anti coagulant medication) excess, plasma protein deficiencies, and treatment of thrombotic thrombocytopenic purpura. Fresh frozen plasma should not be used routinely to replace/expand blood volume. As fresh frozen plasma does not contain any cellular material, it does not transmit infections which are transmitted by cellurar components, e.g. CMV (cytomegalovirus).

Cryoprecipitate:

Cryoprecipitate can be used to supply coagulation factors such as factor-VIII, fibrinogen, von Willebrand factor (vWF) in deficiency states. Each unit of cryoprecipitate can supply 30 units of factor VIII, if factor VII concentrate is not available. Cryoprecipitate may also be used in treatment of von Willebrand disease, where von Willebrand factor may be absent.

Plasma Derivatives:

Plasma is pooled from thousands of donors and specific plasma derivatives such as plasma proteins (albumin, immunoglobulins), antithrombin, and coagulation factorsare produced.

Specific plasma derivatives are also prepared from pooled plasma from donors with high concentration of antibodies against specific diseases such as anti-D, and antisera to hepatitis B virus (HBV), varicella-zoster virus, CMV, and other infectious agents.