Review notes part 4: Blood Bank Compatibility Testing Protocols, IAT Crossmatching, and Patient Case Analysis

Principles of ABO/Rh Typing and Antiglobulin Testing

• Primary ABO and Rh blood typing reagents determine the patient antigen profile:

  • Anti-A reagent reaction: $4+$ agglutination.

  • Anti-B reagent reaction: $0$ agglutination.

  • Anti-D reagent reaction: $3+$ agglutination.

  • Resulting blood type: A positive (A Rh-positive) for Mr. Landsteiner.

• Direct Antiglobulin Test (DAT) versus Indirect Antiglobulin Test (IAT):

  • Direct Antiglobulin Test (DAT): Detects antibodies or complement components bound to red blood cells in vivo.

  • Indirect Antiglobulin Test (IAT): Detects antibodies bound to red blood cells in vitro.

  • Autocontrol and DAT positivity: A patient autocontrol and DAT may test positive due to autoantibodies or transfused donor cells reacting with patient plasma in vivo. Autocontrol is mainly used for AB, D-positive patients to ensure that there was no spontaneous agglutination that will cause false-positive reactions.

Phases of Indirect Antiglobulin Test (IAT) Crossmatching

• Immediate-Spin (IS) Phase:

  • Primary Purpose: Done specifically to detect $\text{IgM}$ antibodies.

  • Clinical Significance: $\text{IgM}$ antibodies are generally not clinically significant unless they belong to ABO blood group antibodies.

  • Immunogenicity Note: Anti-D antibodies are the most immunogenic and can be highly clinically significant.

• $37\,^{\circ}\text{C}$ Incubation Phase:

  • Centrifugation after incubation is performed ONLY if Polyethylene Glycol (PEG) is NOT being used in the procedure.

  • Purpose: Assists in detecting very strong Rh antibodies.

• Anti-Human Globulin (AHG) Phase:

  • Addition of monospecific AHG helps specifically in detecting $\text{IgG}$ antibodies.

  • Clinical Protocol: When crossmatching recipients with clinically significant antibodies, antigen-negative donor units are mandatory, and a full AHG crossmatch (Full AHG Xm) must be performed.

Requirements for Electronic and Computer Crossmatching

• Computer System Standards:

  • Electronic crossmatching (Electronic Xm) is performed using laboratory computers equipped with AABB standard-approved software.

  • Serves as the final verification check of ABO compatibility between recipient and donor.

• Mandatory Patient Criteria for Electronic Crossmatch:

  • Criterion $1$: The patient must have $2\,\text{specimens}$ collected at different times.

  • Criterion $2$: The ABO/Rh blood types obtained from both specimens must be identical.

  • Criterion $3$: Both collected specimens must yield a negative antibody screen ($0$ agglutination).

  • Criterion $4$: The laboratory computer algorithm must possess verified logic to detect incompatible ABO blood groups.

  • Criterion $5$: The patient must have historical records established in the database.

Compatibility Criteria and Interpretation Guidelines

• Full Crossmatch (Full Xm) Compatibility Standard:

  • In order for recipient plasma and donor red blood cells to be determined compatible, the full crossmatch test must demonstrate:

  • Absolute absence of agglutination ($0$ reaction grade).

  • Absolute absence of hemolysis across all testing phases.

Clinical Case Analyses and Critical Thinking

• Patient $1$ Case Evaluation:

  • Patient Demographics: $54\,\text{years old}$ male.

  • Transfusion History: Received $2\,\text{RBC units}$ $5\,\text{years ago}$.

  • Antibody History: No history of previous red cell antibodies.

  • Current Antibody Screen: Negative ($0$ reaction grade).

  • Required Crossmatch Test: Immediate-spin (IS) crossmatch to detect $\text{IgM}$ antibodies. An Electronic Xm may be utilized if the blood types are identical across $2\,\text{specimens}$ collected at different times or confirmed from a different hospital.

• Patient $2$ Case Evaluation:

  • Patient Demographics: $48\,\text{years old}$ male.

  • Transfusion History: Received $3\,\text{RBC units}$.

  • Antibody History: Documented history of anti-S (anti-Ska) antibody.

  • Current Antibody Screen Results:

  • Screen Cell $1$: IS = $0$, $37\,^{\circ}\text{C}$ = $0$, IgG = $1+$, Check Cells (CC) = Not Tested ($\text{NT}$) / $0$.

  • Screen Cell $2$: IS = $0$, $37\,^{\circ}\text{C}$ = $0$, IgG = $3+$, Check Cells (CC) = Not Tested ($\text{NT}$) / $0$.

  • Screen Cell $3$: IS = $0$, $37\,^{\circ}\text{C}$ = $0$, IgG = $1+$, Check Cells (CC) = $0$.

  • Polyspecific AHG testing evaluates both IgG and C3 complement component reactivity.

  • Required Crossmatch Test: Full AHG crossmatch using confirmed antigen-negative donor units due to the documented history of anti-S antibody.

• MSBOS- Maximum Surgical Blood Order Schedule - A protocol designed to ensure that the appropriate blood product is available for patients undergoing surgical procedures, minimizing the risk of delays in transfusion. This is the means we work to conserve blood products

• Adsorption-This technique is used to suck the antibodies out of the plasma and red cells and repeat the antibody screen to detect any alloantibodies. If there is a high incidence antigen found, it would be after this adsorption test and the antibody screening would yield the same results as before the adsorption.