Blood allergies, also known as hypersensitivity reactions to blood transfusions or blood products, are primarily caused by an immune response to antigens present in the transfused blood. When the recipient's immune system recognizes these antigens as foreign, it triggers an allergic reaction.
Here's a more detailed breakdown:
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Antigen-Antibody Reaction: The recipient's immune system produces antibodies (specifically IgE antibodies in some cases) against antigens present in the donor blood. These antigens can be on the surface of red blood cells, white blood cells, platelets, or even plasma proteins.
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IgE and Mast Cell Activation: In some cases, the allergen (antigen in the blood) binds to IgE antibodies already present on the surface of mast cells and basophils. This binding triggers these cells to release histamine and other inflammatory chemicals.
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Histamine Release: Histamine causes various symptoms, including:
- Constriction of airways, making breathing difficult.
- Dilation of blood vessels, leading to a drop in blood pressure.
- Increased permeability of blood vessels, causing swelling (hives).
- Itching.
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Other Immunological Mechanisms: Besides IgE-mediated reactions, other immune mechanisms can contribute to blood allergies, including complement activation and reactions mediated by other types of antibodies (e.g., IgG).
Common Blood Allergy Triggers:
While any component of donor blood can potentially trigger an allergic reaction, some common culprits include:
- Plasma Proteins: Proteins present in the plasma portion of the blood can sometimes elicit an allergic response.
- White Blood Cells (Leukocytes): Reactions to white blood cells can lead to febrile non-hemolytic transfusion reactions (FNHTRs), which, while not always strictly allergic, involve immune activation.
- Red Blood Cell Antigens: While often leading to hemolytic transfusion reactions (where red blood cells are destroyed), incompatible red blood cell antigens can sometimes contribute to allergic-type symptoms.
- IgA Deficiency: In rare cases, individuals who are IgA deficient can develop antibodies against IgA. Receiving blood products containing IgA can trigger an anaphylactic reaction.
Symptoms of Blood Allergies:
Symptoms can range from mild to severe and may include:
- Hives (urticaria)
- Itching (pruritus)
- Flushing
- Swelling (angioedema)
- Difficulty breathing (dyspnea)
- Wheezing
- Low blood pressure (hypotension)
- Anaphylaxis (a severe, life-threatening allergic reaction)
Diagnosis and Treatment:
Blood allergies are diagnosed based on symptoms, medical history, and sometimes specific blood tests. Treatment depends on the severity of the reaction and may involve:
- Stopping the transfusion immediately.
- Administering antihistamines to block the effects of histamine.
- Giving corticosteroids to reduce inflammation.
- Providing epinephrine (adrenaline) for severe reactions like anaphylaxis.
- Oxygen therapy to support breathing.
Prevention strategies, such as using leukoreduced blood products (blood with white blood cells removed) or washing blood components to remove plasma proteins, can reduce the risk of allergic transfusion reactions.
In summary, blood allergies stem from the recipient's immune system reacting to foreign antigens in the transfused blood, leading to the release of inflammatory chemicals like histamine and causing various allergic symptoms.
