Immunohematology Final Exam Study Notes

Final Exam Review for Principles of Immunohematology

Overview of Exam Content

  • The final exam is comprehensive, covering various concepts learned throughout the course.

  • Areas of focus include:

    • Screening cells and ID cells

    • Antigens and blood typing

    • Homologous vs. heterologous considerations

    • Testing methodologies

Screening Cells and ID Cells

  • Blood Type Requirements:

    • Screening cells must be group O.

    • Reason: Group O is the universal donor; it lacks A and B antigens, minimizing potential reactions in recipients.

  • Antigens Present on Red Cells:

    • Must determine specific antigens present on screening cells.

Genetic Concepts

  • Heterozygous vs. Homozygous:

    • Definitions:

    • Homozygous: An individual inherits the same allele from both parents; e.g., for antigen JKA, a homozygous individual has JKA/JKA.

    • Heterozygous: An individual inherits different alleles from each parent; e.g., for antigens JKA and JKB, a heterozygous individual has JKA/JKB.

  • Dosage Effects:

    • Can influence the strength of antibody reactions.

Tests in Immunohematology

  • Indirect Antiglobulin Test (IAT):

    • Used for antibody screening and identification.

    • Principle: Detects antibodies present in plasma.

  • Direct Antiglobulin Test (DAT):

    • Detects antibodies bound to red cells.

    • Usage: Determines if antibodies are present on red blood cells, simplest interpretation being an auto control.

    • Check Cells: If control check cells test fails:

    • Likely due to inadequately washed cells.

Antibody Identification

  • Alloantibody vs. Autoantibody:

    • Alloantibody: An immune response from exposure to foreign red cells (e.g., pregnancy, transfusions).

    • Detected via positive auto control.

    • Autoantibody: Produced against the body's own cells due to autoimmune issues.

Agglutination Mechanisms

  • Antibody-Antigen Binding:

    • Binding leads to agglutination, essential for blood typing.

Potentiators Used in Testing

  • Low Ionic Strength Solution (LIS):

    • Enhances antibody binding by reducing zeta potential, improving agglutination.

  • Polyethylene Glycol (PEG):

    • More sensitive than LIS, helps concentrate antibodies and increase reactiveness.

  • Albumin:

    • Less effective, requiring longer incubation times.

Blood Group Determination

  • Use of Punnett Squares:

    • Visual representation for predicting genotypic and phenotypic blood group inheritance.

Phases of Reaction

  • Temperature Effects:

    • Antibodies exhibit different activities in various temperatures:

    • Immediate Spin: Cold antibodies, typically IgM.

    • 37°C Phase: Warm antibodies, typically IgG.

ABO Blood System

  • Immunodominant Sugars:

    • Key sugars that determine the ABO blood group phenotypes.

  • Bombay Phenotype:

    • Unique blood type lacking A and B antigens, leading to possible transfusion complications.

Rh Factor Considerations

  • Fisher Race System vs. Wiener System:

    • Different systems to classify Rh antigens, understanding both is crucial for accurate blood typing.

  • Weak D Phenotype Testing:

    • Use IAT to determine weak D status and implications for transfusion compatibility.

Secretor Status

  • Secreters vs. Non-Secreters:

    • Genetic variations dictate whether Lewis antigens are present on red cells vs. saliva.

Subgroups of A Blood Type

  • Testing for A Subgroup:

    • Test for anti A1; a positive result indicates A1 subgroup, whereas a negative result necessitates further investigation of other subgroups.

Antigen Presence in Hemolytic Disease

  • Lewis System:

    • Does not affect hemolytic disease in the fetus as Lewis genes must be absorbed.

Miscellaneous Blood Group Systems

  • XGA, Donath-Landsteiner Antibody:

    • Brief overview of these rare antibodies and their implications.

Immunoglobulin Overview

  • Types of Antibodies:

    • IgG: Clinically significant, pertinent in Rh and many alloantibody reactions.

    • IgM: Primarily involved in cold agglutination.

Blood Product Transfusion Considerations

  • Types of Blood Products Used:

    • Anemia: Packed red blood cells.

    • Hemophilia: Factor replacements or cryoprecipitate.

  • Factors to Evaluate:

    • Patient transfusion history, number of pregnancies, and immune reactions.

Blood Product Handling

  • Expiration Dates:

    • Cryoprecipitate and Platelets: Expire in four hours upon pooling.

    • Fresh Frozen Plasma: One year, or twenty-four hours once thawed.

  • Irradiation:

    • Used to prevent graft-versus-host disease, retains safety for immunocompromised patients.

  • Exchange Transfusion:

    • Specific criteria for receiving babies: O negative, CMV negative, less than seven days old, must be compatible with maternal blood, and negative for hemoglobin S.

Testing Methodologies

  • Comparison of Testing Methods:

    • Gel Testing: Utilizes column agglutination.

    • Solid Phase Testing: Differences in sensitivity and ease of use compared to tube tests.

Conclusion

  • For further questions regarding these topics, students are encouraged to reach out via email for clarification or additional study materials.