📚 Hematology — L9: Blood Transfusion Medicine

📚 Lecture Overview

This lecture covers blood transfusion medicine, detailing blood group systems, compatibility rules, and various blood components along with their specific clinical indications. It also explores the broad spectrum of transfusion-related complications, categorizing them into immediate vs. delayed and immune vs. non-immune reactions. Understanding these concepts is vital for ensuring safe transfusions and promptly managing life-threatening adverse events.

🎯 Key Concepts & Definitions

• Blood Compatibility: The requirement that blood components containing > 2 ml of RBCs must be compatible with the recipient’s plasma to prevent acute hemolysis.
• Platelet Refractoriness: The lack of a sufficient increase in platelet count following two successive adequate single donor platelet transfusions, caused by immune or non-immune mechanisms.
• Massive Transfusion: The administration of blood components over a 24-hour period equaling or exceeding the total blood volume ($≥$ 10 units of whole blood or 20 units of packed RBCs in an adult).
• Leukodepletion: The removal of white blood cells from blood products to reduce complications like FNHTR and CMV transmission.
• Alloimmunization: The immune system's development of antibodies against foreign antigens introduced via transfusion or pregnancy.

📖 Main Content

1. Blood Components and Derivatives

• Whole Blood:
• Stored at 4⁰C (2-6⁰C) for up to 35 days.
• Indications: Acute hypovolemia with RBC loss, and exchange transfusion (e.g., sickle cell crises, HDN).
• Lacks functional platelets and granulocytes (deteriorate in < 24 hours).
• Packed RBCs:
• Indications: Treatment of symptomatic anemia.
• One unit increases Hb by 1 g/dl in an average-sized adult.
• Platelets:
• Stored at room temperature on a platelet shaker for up to 5 days.
• One unit increases platelet count by 5,000-10,000/cmm3.
• Prophylactic thresholds: Major surgery $≤$ 50; Ocular/Neurosurgery $≤$ 100; Stable/afebrile < 10; Stable with temp >38⁰C < 20.
• Fresh-Frozen Plasma (FFP):
• Stored frozen at –20⁰C to –80⁰C for up to one year.
• Indications: Correction of multiple clotting factor deficiencies, DIC, liver disease, massive transfusions, TTP (plasma exchange), and rapid warfarin reversal.
• Cryoprecipitate:
• Contains factor VIII, fibrinogen, factor XIII, and vWF activity.
• Indications: Fibrinogen deficiency, factor XIII deficiency, DIC, and urgent treatment of hemophilia A or von Willebrand disease if specific concentrates are absent.
• Blood Derivatives: Commercially produced via plasma fractionation, heat/chemically treated to eliminate viruses. Includes Albumin, IVIG, Rh immune globulin, and Recombinant coagulation factors.

2. Immediate Immunological Complications

• Febrile Non-Hemolytic Transfusion Reaction (FNHTR):
• Most common reaction; defined by > 1°C increase in temperature.
• Caused by passive transfer of donor cytokines (pyrogens). Managed with antipyretics and prevented by leukodepletion.
• Mild Allergic/Urticarial Reactions:
• Localized erythema, pruritus, and urticaria mediated by IgE antibodies against donor plasma proteins. Managed with antihistamines.
• Anaphylactic Transfusion Reactions:
• Severe respiratory distress and shock occurring in IgA-deficient patients possessing anti-IgA antibodies. Managed with adrenaline and corticosteroids.
• Acute Hemolytic Transfusion Reaction (AHTR):
• Caused by ABO incompatibility (mismatched blood).
• Mediated by pre-formed IgM isohemagglutinins causing intravascular hemolysis, hemoglobinemia, hemoglobinuria, renal failure, and shock. Requires immediate cessation and aggressive fluid resuscitation.
• Transfusion-Related Acute Lung Injury (TRALI):
• Non-cardiogenic pulmonary edema developing within 6 hours.
• Caused by donor leukoagglutinins (anti-HLA or granulocyte antibodies) injuring the pulmonary endothelium. Most common donors are multiparous females.

3. Delayed Immunological & Non-Immunological Complications

• Delayed Hemolytic Transfusion Reaction (DHTR):
• Occurs 1-3 weeks post-transfusion via anamnestic response; presents as fever, hyperbilirubinemia, and anemia with a positive DAT (extravascular hemolysis).
• Post-Transfusion Purpura (PTP):
• Sudden profound thrombocytopenia 5-10 days post-transfusion due to anti-HPA-1a antibodies attacking platelets.
• Transfusion-Associated Graft versus Host Disease (TA-GvHD):
• Caused by donor lymphocytes attacking host tissues in immunocompromised patients. Prevented by $\gamma$-irradiation of blood components (2500 cGY). Leukoreduction does not prevent it.
• Circulatory Overload (TACO):
• Cardiogenic pulmonary edema in vulnerable patients. Prevented by slower infusion rates (1-4 ml/kg/H).
• Bacterial Contamination:
• Platelets kept at room temperature are highly susceptible to bacterial growth (Staphylococci, Streptococci). RBCs cold-stored can harbor Yersinia or Pseudomonas.
• Transfusional Iron Overload (Hemosiderosis):
• Occurs after > 20 blood transfusions. Managed with iron chelation therapy when ferritin > 1000 ng/ml.

4. Massive Transfusion Sequelae

• Defined as $≥$ 10 units of whole blood or 20 units of PRBCs in 24 hours.
• Complications:
• Hypothermia: Prevented by blood warmers.
• Coagulopathy (Dilution/DIC): Prevented by balanced transfusion (1 unit blood : 1 unit platelets : 1 unit FFP).
• Acidosis: Managed with sodium bicarbonate.
• Electrolyte shifts: Hypocalcemia and Hypomagnesemia due to citrate binding (treated with IV calcium/magnesium); Hyperkalemia from stored RBC potassium (treated with insulin and glucose).

📊 Visual Learning

💡 Important Points to Remember

• Packed RBCs increase adult Hb by exactly 1 g/dl per unit.
• Platelets are stored at room temperature (5 days max); RBCs and whole blood are refrigerated at 2-6⁰C (up to 35 days).
• AHTR is mediated by IgM antibodies causing intravascular hemolysis with hemoglobinuria; DHTR involves extravascular hemolysis with a positive DAT and no hemoglobinuria.
• TRALI is non-cardiogenic pulmonary edema triggered by donor antibodies, frequently from multiparous females.
• TA-GvHD is prevented exclusively by $\gamma$-irradiation, not by leukoreduction.
• Massive transfusion requires balanced component replacement (1:1:1 ratio of blood, platelets, and FFP) to prevent dilutional coagulopathy and DIC.
• Citrate toxicity during massive transfusion binds calcium and magnesium, causing hypocalcemia and hypomagnesemia.
• Platelet refractoriness is defined as a lack of response to two successive adequate single donor platelet transfusions.

⚠️ Common Exam Questions

• Classic MCQ Trick: Examiners often ask how to prevent TA-GvHD and list "Leukoreduction" as a distractor. Remember: Leukoreduction prevents FNHTR and CMV, but only $\gamma$-irradiation prevents TA-GvHD.
• Scenario Question: A patient develops sudden hypotension, fever, and bilateral pulmonary infiltrates within 6 hours of receiving blood from a multiparous female donor. Examiners will test your ability to differentiate TRALI (non-cardiogenic, donor leukocyte antibodies) from TACO (cardiogenic overload, slow rate needed).
• Hemolysis Differentiation: Test questions frequently contrast AHTR (immediate, IgM, intravascular hemolysis with hemoglobinuria) against DHTR (1-3 weeks later, extravascular hemolysis, positive DAT, no hemoglobinuria).

📝 Quick Review Checklist

I can identify the storage conditions and shelf-life of different blood components
I understand the distinct clinical indications for FFP versus Cryoprecipitate
I can differentiate between immediate immune reactions (FNHTR, AHTR, TRALI, Anaphylaxis)
I know the underlying mechanism and prevention of TA-GvHD ($\gamma$-irradiation)
I can list the key metabolic and electrolyte complications of massive transfusion
I can distinguish between intravascular (AHTR) and extravascular (DHTR) hemolysis