Immunopathology and Transfusion Medicine
Immunopathology and Transfusion Medicine tests hypersensitivity, autoimmunity, immunodeficiency, transplant rejection and blood-bank safety. The exam links immune mechanisms to tissue injury and to bedside transfusion decisions.
Core rules
- Type I hypersensitivity is IgE-mediated immediate allergy; type II is antibody against fixed antigen; type III is immune-complex deposition; type IV is T-cell-mediated delayed hypersensitivity.
- Autoimmune disease reflects loss of tolerance; diagnosis combines clinical features, autoantibodies and tissue biopsy.
- Transplant rejection: hyperacute is preformed antibody; acute cellular is T-cell-mediated; acute antibody-mediated is donor-specific antibody; chronic is fibrosis and vascular change.
- ABO compatibility is critical. Type and screen detects ABO/Rh and unexpected antibodies; crossmatch confirms compatibility.
- Acute hemolytic transfusion reaction is usually ABO incompatibility; delayed hemolytic reaction is often an anamnestic antibody response.
Worked example
A patient develops fever, flank pain and hemoglobinuria minutes after starting a red-cell transfusion. The likely diagnosis is acute hemolytic transfusion reaction from ABO incompatibility. Reasoning: symptoms begin during transfusion, and intravascular hemolysis releases hemoglobin. Stop the transfusion, support airway and circulation, maintain urine output, send samples for hemolysis and compatibility testing, and report the event.
Traps
Do not confuse TRALI with TACO: TRALI is noncardiogenic pulmonary edema with fever and hypotension; TACO is volume overload with hypertension. A negative antibody screen does not replace bedside identity checks. Graft-versus-host disease is mediated by donor T cells, not host rejection.