Blood Banking Procedures

Blood Banking Procedures – Detailed Study Notes

1. Big Picture of Pretransfusion Testing

  • Goal: Provide the safest compatible blood product for patients.
  • Routine Pretransfusion Workup Includes:
    • Patient identification
    • Specimen verification
    • ABO/Rh typing
    • Antibody screen
    • Review of transfusion and pregnancy history
    • Crossmatch selection
  • Extra Workup: Required if a clinically significant antibody is suspected or detected before blood issuance.
  • Correlations: Laboratory findings must be correlated with patient history, recent transfusions, pregnancy history, medications, diagnosis, and signs of hemolysis.

2. Direct Antiglobulin Test (DAT)

  • Purpose: Detects in vivo coating of red cells with IgG and/or complement.
  • Principle:
    • Patient red cells are washed to remove unbound serum proteins.
    • Anti-human globulin reagent is added.
    • Agglutination indicates attachment of antibody and/or complement to red cells in the body.
  • Common Uses:
    • Suspected hemolytic transfusion reaction
    • Autoimmune hemolytic anemia
    • Hemolytic disease of the fetus and newborn
    • Drug-induced immune hemolysis
    • Evaluation of unexplained hemolysis, jaundice, or anemia
  • Specimen and Method:
    • EDTA blood is preferred to limit complement binding after collection.
    • Red cells washed 3–4 times before AHG is added.
    • Use polyspecific AHG first, then monospecific anti-IgG and anti-C3 if necessary.
    • Validate negative tests with check cells.

3. DAT Result Interpretation

  • Positive with anti-IgG: Cells are coated with IgG; seen in warm autoantibodies, alloantibodies coating transfused cells, and hemolytic disease of the fetus and newborn (HDFN).
  • Positive with anti-C3: Indicates complement coating; may occur with cold-reactive antibodies or some drug-related responses.
  • Positive with both: Both immunoglobulin and complement are attached to red cells.
  • Negative: No detectable coating or below test sensitivity.
  • Pitfalls:
    • Poor washing can lead to false negatives due to neutralization of AHG.
    • Recently transfused patients may present mixed red cell populations.
    • A positive DAT alone does not confirm active hemolysis; results must correlate with clinical findings.

4. Antibody Screen

  • Purpose: Detect unexpected antibodies in patient serum or plasma that may react with donor red cells.
  • Principle:
    • Patient serum/plasma tested against reagent screening cells with known antigen profiles.
    • Test is performed in the indirect antiglobulin phase.
    • Agglutination or hemolysis suggests an unexpected antibody may be present.
  • Clinical Importance:
    • Helps prevent hemolytic transfusion reactions.
    • Detects clinically significant alloantibodies before transfusion.
    • Determines whether antibody identification is required.
  • Typical Procedure:
    • Test patient serum/plasma against a 2- or 3-cell screening panel.
    • Observe at immediate spin if applicable, after incubation at 37°C, and at AHG phase as required.
    • Enhancement media options include LISS, PEG, solid phase, or gel.
    • An autocontrol may be utilized when autoantibody is suspected.

5. Antibody Screen Result Patterns

  • All Cells Nonreactive: No unexpected antibody detected, or antibody level too low for detection.
  • One or More Cells Reactive: Unexpected antibody may be present; proceed to identification.
  • All Cells Reactive: Possible autoantibody, antibody to high-incidence antigen, or multiple antibodies identified.
  • Positive Autocontrol: May indicate autoantibody, recent transfusion with coated cells, or drug-related effect.

6. Antibody Identification

  • Purpose: Determines specificity of an unexpected antibody detected in the screen.
  • Basic Process:
    • Test patient serum/plasma against a larger panel of reagent red cells with known antigen profiles.
    • Compare the reaction pattern of patient serum with the antigen makeup of panel cells.
    • Use nonreactive cells to rule out antigens and reactive cells to support possible specificity.
  • Practical Interpretation Steps:
    • Review which cells react and which do not.
    • Use nonreactive cells to eliminate antigens according to policy.
    • Check for common antigen presence in reactive cells absent from nonreactive cells.
    • Monitor for dosage effects and mixed antibody patterns.
    • Confirm with selected cells, enzyme-treated cells, phenotyping, or reference lab confirmation if necessary.
  • High-Yield Concepts:
    • Clinically significant antibodies typically react at 37°C and/or during AHG phase.
    • Dosage: Some antibodies react more strongly with homozygous antigen expression.
    • Panreactivity can suggest autoantibody, high-incidence antigen, or multiple antibodies.
    • Recent transfusions can complicate interpretation as donor cells may still circulate.

7. Antigen Phenotyping

  • Purpose: Determines if a patient or donor red cell sample possesses a specific antigen.
  • Uses:
    • Supports antibody identification.
    • Identifies antigen-negative donor units.
    • Checks for patient antigens corresponding with suspected alloantibodies.
    • Aids in transfusion planning in chronically transfused patients.
  • Method and Interpretation:
    • Red cells are tested with commercial antisera targeting the antigen of interest.
    • Agglutination indicates presence of the antigen.
    • Absence of agglutination suggests the antigen is not present if controls are valid.
  • Important Limitations:
    • Recent transfusions may cause mixed red cell populations, leading to unreliable results.
    • A positive DAT can interfere with phenotyping interpretation.
    • Some cases might be more accurately assessed through molecular typing.

8. Crossmatches

  • Purpose: Confirms compatibility between patient and selected donor unit before transfusion.
  • Major Types:
    • Immediate Spin: Patient serum combines with donor red cells at room temperature.
    • Used when screen is negative and there are no clinically significant antibodies present.
    • Antiglobulin (Serologic): Incubation through AHG phase.
    • Used when clinically significant antibodies exist or are documented.
    • Electronic: Validated computer check without serologic mixing.
    • Utilized only when ABO/Rh data are confirmed and screen is negative.
  • Interpretation:
    • Compatible: Selected unit may be issued if all other conditions are satisfied.
    • Incompatible: Further investigation necessary before release.
    • Possible Causes of Incompatibility: ABO mismatch, alloantibody, autoantibody, technical error, low-incidence donor antigen.

9. Special Procedures

  • Autocontrol:
    • Patient serum is tested against patient red cells.
    • Helpful to differentiate between alloantibody and autoantibody presence.
    • Positive autocontrol indicates potential autoantibody or coating of patient cells.
  • Elution:
    • Removes bound antibody from red cells to test antibody specificity.
    • Useful in positive DAT scenarios, HDFN, and delayed hemolytic transfusion reactions.
  • Adsorption:
    • Alloabsorption used when recent transfusion complicates results, and autoabsorption can remove warm autoantibody if the patient wasn't recently transfused.
  • Enzyme Treatment:
    • Enzymes like ficin or papain can alter antigen expression, helping to separate antibodies.
    • Antigens such as Rh, Kidd, Lewis, and P1 are often enhanced.
    • Duffy and some MNS antigens may be weakened or destroyed.
  • Neutralization / Inhibition:
    • Soluble substances are employed to neutralize specific antibodies, confirming their specificity.
    • Commonly discussed regarding selected cold-reactive or soluble-substance antibodies.
  • Prewarm Technique:
    • Warms serum, cells, and saline to minimize interferences from cold-reactive antibodies.
    • Useful when cold agglutinins cause broad reactivity.
  • Saline Replacement:
    • Aids in differentiating rouleaux from true agglutination.
    • Particularly relevant for patients exhibiting abnormal plasma proteins.

10. Troubleshooting Patterns

  • Positive Screen, Unclear Panel Fit:
    • Potential Causes: Weak antibody, dosage variations, low-incidence antigen, technical issue.
    • Next Step: Repeat testing, review patient history, consider selected cells or enhanced methods.
  • Panreactive Panel:
    • Potential Causes: Autoantibody, high-incidence antigen, multiple antibodies.
    • Next Step: Check autocontrol and DAT; consider adsorption or reference lab testing.
  • Positive DAT with Hemolysis:
    • Potential Causes: Warm autoantibody, transfusion reaction, HDFN, drug effects.
    • Next Step: Utilize monospecific DAT, perform eluate analysis, and conduct hemolysis workup.
  • Incompatible Crossmatch with Negative Screen:
    • Potential Causes: Low-incidence donor antigen, ABO error, technical issue.
    • Next Step: Repeat ABO verification, re-examine crossmatch, and review donor and patient data.
  • Phenotyping Unreliable:
    • Potential Causes: Recent transfusion, positive DAT.
    • Next Step: Introduce molecular typing or alternative strategies.

11. MT-Level High-Yield Reminders

  • A positive DAT indicates antibody/complement presence on cells; a positive antibody screen indicates antibodies are free in serum/plasma.
  • A historically significant clinically relevant antibody is still important even if not currently detectable.
  • Check cells must validate negative AHG tests.
  • Caution is advised with phenotyping in recently transfused patients.
  • A serologic crossmatch is mandatory when clinically significant antibodies are known or documented.
  • If results do not align, consider recent transfusion, dosage effects, rouleaux, autoantibody presence, and potential technical errors.

12. MT/AAB Exam Preparation Insights

  • AAB MT exam questions often assess knowledge in determining the next best step when test results do not corroborate. The strongest response should integrate serology patterns with the patient’s recent transfusion history and the underlying objectives of procedures.