Preparation of various components of blood for transfusion

Preparing packed red blood cells (PRBCs) and various blood components (fractions) for transfusion involves separating whole blood into different components. Each fraction serves a specific therapeutic purpose, maximizing the utility of donated blood. This process is typically performed in a blood bank or transfusion service laboratory.

Blood Components for Transfusion

1. Packed Red Blood Cells (PRBCs)
2. Platelets
3. Fresh Frozen Plasma (FFP)
4. Cryoprecipitate
5. Plasma-Derived Products

1. Packed Red Blood Cells (PRBCs)

Packed Red Blood Cells are the most common blood product used for transfusion. They are prepared by removing most of the plasma from whole blood, resulting in a concentrated suspension of red blood cells (RBCs). PRBCs increase the oxygen-carrying capacity in patients with anaemia, blood loss, or decreased red cell production.

Preparation of PRBCs:

1. Collection: Whole blood is collected from a donor into an anticoagulant bag, such as CPD (Citrate Phosphate Dextrose).
2. Centrifugation: The whole blood unit is centrifuged at low speed to separate it into three layers:
   • Plasma (Top Layer): Yellowish fluid that contains proteins, clotting factors, and water.
   • Buffy Coat (Middle Layer): A thin layer containing white blood cells (WBCs) and platelets.
   • Red Blood Cells (Bottom Layer): The densest layer containing the red blood cells.
3. Plasma Removal: The plasma and buffy coat are carefully removed, leaving the packed red blood cells at the bottom of the bag.
4. Leukoreduction (Optional): The PRBCs can be filtered to remove white blood cells to reduce the risk of febrile transfusion reactions and transmission of leukocyte-associated viruses.
5. Storage: PRBCs are stored at 1-6°C and have a shelf life of 35 to 42 days, depending on the preservative solution.

Indications for PRBC Transfusion:

• Symptomatic anaemia (e.g., from trauma, surgery, or chronic disease).
• Blood loss due to trauma or surgery.
• Hemoglobin is less than 7-8 g/dL in most patients.
• Haemoglobin less than 10 g/dL in patients with heart disease or respiratory problems.

2. Platelets

Platelet concentrates are prepared from whole blood or by apheresis. Platelets are critical for clotting and are used to prevent or treat bleeding in patients with low platelet counts (thrombocytopenia), platelet dysfunction, or massive transfusion situations.

Preparation of Platelets:

1. Centrifugation: After collecting whole blood, it undergoes light centrifugation to separate the plasma (containing platelets) from the RBCs. The RBCs are set aside, and the plasma is further centrifuged at a higher speed to concentrate the platelets.
2. Pooling: Platelets from multiple whole blood donations (usually 4-6 donors) can be combined to form a single therapeutic dose, called pooled platelets.
3. Apheresis Platelets: Alternatively, platelets can be collected from a single donor through an apheresis machine, which selectively extracts platelets and returns the remaining blood components to the donor. This method provides a single donor platelet concentrate equivalent to a pooled unit.
4. Storage: Platelets are stored at 20-24°C with gentle agitation for 5-7 days.

Indications for Platelet Transfusion:

• Thrombocytopenia (low platelet count) due to bone marrow disorders, chemotherapy, or aplastic anaemia.
• Platelet dysfunction due to medications like aspirin.
• Massive transfusion protocols.
• Active bleeding in patients with platelet counts below 50,000/µL.
• Prophylactic transfusion in patients with platelet counts below 10,000/µL.

3. Fresh Frozen Plasma (FFP)

Fresh Frozen Plasma (FFP) is the liquid portion of blood containing water, electrolytes, proteins (including albumin), clotting factors, and fibrinogen. FFP is primarily used to replace coagulation factors in patients with bleeding disorders.

Preparation of FFP:

1. Collection and Centrifugation: Whole blood is centrifuged to separate the plasma from the red blood cells and buffy coat.
2. Freezing: The plasma is rapidly frozen to -18°C or colder within 8 hours of collection to preserve the clotting factors.
3. Thawing (Before Use): FFP must be thawed before transfusion and used within 24 hours of thawing.
4. Storage: FFP is stored at -18°C or colder for 12 months.

Indications for FFP Transfusion:

• Replacement of multiple coagulation factor deficiencies (e.g., liver disease, disseminated intravascular coagulation).
• Warfarin reversal in the presence of bleeding.
• Massive transfusions.
• Coagulation factor deficiencies when specific concentrates are unavailable (e.g., Factor V deficiency).
• Plasma exchange in thrombotic thrombocytopenic purpura (TTP).

4. Cryoprecipitate

Cryoprecipitate is a component of plasma rich in certain clotting factors, particularly fibrinogen, Factor VIII, von Willebrand factor, and Factor XIII. It treats bleeding due to low fibrinogen levels or certain clotting disorders.

Preparation of Cryoprecipitate:

1. Thawing FFP: FFP is slowly thawed at 1-6°C.
2. Precipitate Formation: During thawing, the clotting factors (mainly fibrinogen and Factor VIII) precipitate out of the plasma.
3. Separation: The precipitated material (cryoprecipitate) is separated from the remaining plasma.
4. Freezing: The cryoprecipitate is refrozen and stored at -18°C or colder.
5. Storage: Cryoprecipitate is frozen and has a shelf life of up to 12 months.

Indications for Cryoprecipitate Transfusion:

• Hypofibrinogenemia (low fibrinogen levels), such as in DIC, liver disease, or massive transfusions.
• Congenital fibrinogen deficiencies.
• Haemophilia A (Factor VIII deficiency) when specific factor concentrates are unavailable.
• Von Willebrand disease.
• Factor XIII deficiency.

5. Plasma-Derived Products

Various therapeutic products can be derived from plasma through fractionation, which separates and purifies different proteins from plasma. Common plasma-derived products include:

• Albumin: Used for volume expansion in hypovolemia, burns, and hypoalbuminemia.
• Immunoglobulins: Used to treat immunodeficiency disorders and autoimmune conditions.
• Coagulation Factor Concentrates: Specific factors such as Factor VIII or IX for treating haemophilia.
• Prothrombin Complex Concentrates (PCC): Used for reversing anticoagulation in patients on warfarin.