ABO Flashcards
is a laboratory test used to determine a person’s blood group based on the presence or absence of A and B antigens on red blood cells (RBCs) and the corresponding antibodies in the plasma.
ABO typing
two main procedures:
- Forward Typing (Direct or Front Type, Shift to the Right Typing)
- Reverse Typing (Back Type, Shift to the Left Typing, Indirect or Serum Typing)
FORWARD TYPING
• Also known as:
Front type, shift to the right typing, direct cell typing
FT
• Purpose:
Detects ABO antigens (A and B antigens) on the patient’s red blood cells
FT
Sample Used:
Patient’s red blood cells (RBCs)
FT
Reagents Used:
Commercially prepared anti-sera (Anti-A, Anti-B, sometimes Anti-D for Rh typing)
FT
Reaction Principle:
• If a patient’s RBCs have the A antigen, they will agglutinate with Anti-A sera
• If the RBCs have the B antigen, they will agglutinate with Anti-B sera
• If neither antigen is present, no agglutination will occur in both Anti-A and Anti-B sera
• If both antigens are present, agglutination will occur in both
RT
• Reagents Used:
Known red cells (A1 cells and B cells)
RT
• Also known as:
Back type, shift to the left typing, indirect or serum typing
RT
• Purpose:
Detects ABO antibodies (Anti-A and Anti-B) in the patient’s plasma
RT
• Sample Used:
Patient’s plasma or serum
RT
Reaction Principle:
• If a patient’s plasma contains Anti-A antibodies, it will agglutinate with A1 cells
• If a patient’s plasma contains Anti-B antibodies, it will agglutinate with B cells
• If no antibodies are present, no agglutination occurs
Why Perform Both Forward and Reverse Typing?
• Forward typing alone can identify ABO antigens, but not antibodies.
• Reverse typing confirms the result by checking for corresponding antibodies in plasma.
• The two tests should be consistent with each other to ensure accurate blood typing.
• Discrepancies between forward and reverse typing must be investigated before issuing blood.
is the clumping of red blood cells due to_____.
Agglutination
antigen-antibody binding
Agglutination
It is graded based on the____ and ______
size of the agglutinates and the clarity of the background
4+
Red cell button is a solid agglutinate with a clear background
3+
Several large agglutinates with a clear background
2+
Many medium-sized agglutinates with a clear background
1+
Medium- and small-sized agglutinates with a turbid (cloudy) background due to many free RBCs
0
(Negative) No visible agglutination; red cells flow freely when resuspended
require further investigation (e.g., weak subgroups, transfusion history).
Weak or mixed-field reactions
is the clumping of red blood cells (RBCs) caused by the interaction of antigens on the RBC membrane with specific antibodies.
Hemagglutination
This reaction is crucial in blood typing, crossmatching, and detecting antibodies in serological testing.
The degree of agglutination provides information on the strength of antigen-antibody interactions.
Hemagglutination
Why is Grading Important?
• Standardization: Ensures uniform interpretation across different laboratories.
• Clinical Relevance: Helps in detecting weak antibodies or weak antigen expressions.
• Troubleshooting: Identifies issues like mixed-field reactions or rouleaux formation.
is always considered a positive reaction, as it indicates the destruction of RBCs by antibodies (e.g., in hemolytic transfusion reactions).
• Hemolysis (H)
suggest weak reactions, requiring further evaluation.
• Lower grades (W+ and 1+)
• indicate strong antigen-antibody reactions.
Higher grades (3+ and 4+)
H (Hemolysis)
Presence of free hemoglobin in the serum (RBC lysis)
10
4+ One solid aggregate (complete agglutination, no free cells)
10
3+ Several medium to large aggregates with no free cells
8
2+ Many small to medium aggregates, clear background
5
1+ Many small aggregates, turbid background
3
+ or W+ (Weak Positive) Few small aggregates, mostly unagglutinated cells
+m or +m (Microscopic Agglutination) Aggregates only visible under a microscope
1
0 (Negative) No visible aggregates, all cells remain unagglutinated
0
Red cells appear as stacks of coins, a nonspecific aggregation Not a true agglutination; disappears upon adding saline
R (Rouleaux Formation)
Presence of two cell populations, one agglutinated and one free May occur in recent transfusions, chimerism, or weak subgroups
mf (Mixed-Field Agglutination)
In blood banking,______ is considered a strong positive reaction because it indicates complement activation and RBC destruction.
hemolysis
How to Differentiate in the Lab?
Agglutination vs Hemolysis
• Perform a saline wash or saline replacement test: Rouleaux will disperse in saline, while true agglutination remains.
• Microscopic examination: Rouleaux appears as stacks of coins, whereas agglutination looks like clumps of irregularly shaped cells.
Why Wash RBCs?
• To remove plasma proteins, fibrin, and interfering substances that can cause false reactions.
• To eliminate substances like fibrin strands, rouleaux-inducing proteins, and hemolysis-inducing contaminants.
How to Wash RBCs?
• Add normal saline (NSS) to the pRBCs.
• Mix gently by inverting the tube.
• Centrifuge for 3 minutes at 1000-2000g.
• Discard the supernatant carefully without disturbing the cell button.
• Repeat the process for a total of 3 washes.
Why is the Tube Method More Accurate?
The tube method provides better sensitivity and specificity than the slide method because:
• It allows better mixing of reagents.
• It uses centrifugation, which enhances weak reactions.
• It reduces false-negative results that may occur in slide testing.
