3. Blood Bank Reagents and Equipment

  • Blood typing reagents: Used to determine blood group and compatibility for transfusions.

  • Antisera: Solutions containing antibodies for blood group typing, including anti-A, anti-B, and anti-D.

  • Centrifuge: Device used to separate blood components by density, crucial for processing samples.

  • Blood bags: Sterile containers for collection and storage of blood and blood products, designed for safe transport.

Potency versus Specificity
Potency

  • Definition: Refers to the "strength" of a reagent.

  • Measurement: Indicates how strongly the reagent will react with its corresponding antigen or antibody, measured by the strength of agglutination.

  • Reporting: Serological agglutination is measured and reported as:

    • 4+, 3+, 2+, 1+ (dependent upon the size of the button for positive reactions).

    • 0 is reported for negative reactions; never use the symbol “–” for negative results.

  • Factors Affecting Potency:

    • Antibody concentration (titre).

    • Reagent preservation (additives, buffers, etc.).

    • Storage conditions and expiration (correct temperature, proximity to end of shelf life).

Specificity

  • Definition: Refers to the ability of a reagent to react only with its intended antigen or antibody.

  • Expected Reactions:

    • Example:

    • Anti-A antisera should NOT agglutinate B antigens.

    • Anti-A antisera will ONLY agglutinate A antigens.

  • Importance: Prevents false-positive results and ensures accurate antigen typing or antibody identification; high specificity ensures reactions are meaningful and interpretable.

Reagent Quality Control

  • Regular QC: Usually performed daily, must meet minimum reactivity standards set by manufacturers and regulatory bodies.

  • Verification Includes:

    • Potency: Expected reaction strength with KNOWN positive cells.

    • Specificity: No reaction with KNOWN negative cells.

  • Interpretation of Results:

    • If agglutination results are less than 3+ (e.g., anti-A shows 2+ or 1+), it may indicate deteriorating reagent potency.

    • This deterioration may compromise detection of A antigens in patient samples.

    • Failure in either or both parameters makes the reagent unacceptable for patient testing, necessitating appropriate corrective action, which must be implemented and documented.

Reagents Used for ABO Testing

  • Definitions:

    • Anti: Means antibody.

    • Anti-A and Anti-B: Commercial reagents known as antisera (known antibody) used to determine the presence or absence of A or B antigens of the ABO blood group system.

  • Procedure:

    • Patient or blood donor cells (unknown antigens) are added to the known antibodies – A and B antisera.

    • The cells and antisera are mixed, centrifuged, and observed for the presence or absence of agglutination.

    • Agglutination indicates that the specific antigen is present due to reaction with its specific antibody.

  • Example:

    • Patient X red cells added to anti-A results in 4+ agglutination.

    • Patient X red cells added to anti-B results in NO agglutination.

    • Conclusion: Patient X only has the A antigen on their red cells and is classified as Group A.

ABO Forward Typing/Grouping

  • Forward Testing: Determines which ABO antigens are present on patient or donor red blood cells.

    • The presence or absence of A and B antigens determines blood group (blood type).

  • Reverse Typing: Confirms forward typing by determining the ABO antibodies present in patient or donor cells based on their red cell antigens.

    • Individuals cannot possess antibodies against antigens they have on their red cells.

  • Discrepancies: If forward and reverse tests do not correlate, results are deemed discrepant, and emergency O Negative units are transfused.

  • Limitations: Can be affected by age, certain immunocompromised states (e.g., due to HIV or kidney transplant), leading to potential non-production of expected antibodies.

Reagents for ABO Forward Typing
Anti-A

  • Used in ABO Forward testing to determine the presence/absence of A antigen on RBC surface.

  • Method: Direct testing; patient RBCs added to antisera, spun, and read.

  • Results:

    • Agglutination indicates presence of A antigen (graded 1+ to 4+).

    • No agglutination indicates a negative result (graded as 0).

Anti-B

  • Similar application as Anti-A.

  • Different reagent color (yellow dye).

  • Used to determine presence/absence of B antigen.

Anti-A,B

  • Used in ABO Forward testing, determining presence/absence of both A and B antigens.

  • This reagent is primarily used to confirm weak subgroups of A or neonatal samples and to resolve discrepancies.

Reverse ABO Testing

  • Definition: Determines ABO antibodies present in the patient's blood, mainly IgM and do not require prior exposure to develop.

  • Testing Cells: Commercially prepared cells of known antigen content labeled A1 and B pooled cells.

  • Buffer Solution: Used to preserve cells, minimize hemolysis, and maintain antigenicity.

  • Theory: Patients possess antibodies against the antigens lacking on their red cells (Landsteiner’s Rule).

  • Example: Group B individuals will have anti-A antibodies but lack A antigens on their red cells.

Rh Testing/Typing

  • Description: Determines the presence or absence of the D antigen; crucial in blood bank testing due to its role in HDFN and HTR.

  • Testing Method: Patient RBCs + anti-D, spin, and read.

  • Results:

    • Agglutination indicates D antigen present (Rh Positive).

    • No agglutination indicates absence of D antigen (Rh Negative).

    • Results should always be recorded as Rh Positive or Rh Negative, not Rh+ or Rh–.

Reagents for Rh Antigen Typing
Anti-D Antisera

  • Distinguishes between Rh-Positive and Rh-Negative individuals.

  • Must run Rh control in parallel to avoid false-positive results.

Control Antisera

  • Rh control (anti-RHC) contains only high protein diluent, no D antibody, to control for false positives in Rh results.

Production and Differences Between Polyclonal and Monoclonal Antibodies
Polyclonal Antibodies

  • Antibodies with different affinities for the same antigen but different epitopes.

  • Preparation:

    • An antigen is injected into an animal (mouse, rabbit, goat) activating B-lymphocytes.

    • The animal’s serum is collected, and IgG immunoglobulins are purified.

Monoclonal Antibodies

  • Identical antibodies produced from a single clone of B cell specific to one epitope.

  • Production:

    • Requires the creation of a hybridoma by fusing a specific plasma cell with myeloma cells.

    • Hybridomas are immortal and produce identical antibodies indefinitely.

Quality Control in Blood Bank Reagents

  • Ensuring accuracy, potency, and specificity of commercial anti-sera and cells.

  • Daily/weekly testing procedures with known controls, visual inspections for turbidity or contamination.

  • Documentation: Ensures traceability, confirms testing dates, and supports patient safety.

Preparation of Reagents and Cells

  • Follow proper rehydration and suspension procedures, equilibrate reagents to room temperature, and store as specified.

  • Safety Practices: Avoid contamination, never touch tips with fingers, and do not return unused reagents to stock.