Grouping

Screening

Antibody ID

GROUPING

ABO BLOOD GROUP SYSTEM

For all donors and recipients, ABO blood groups are determined to ensure that blood of the same or a compatible ABO type is used for transfusion.

The unique feature of the ABO system is the presence of complementary antibodies in individuals with group A, B and H(O) antigens on their red cells. Individuals of group A have antibody to blood group B in their serum. Individuals of blood group B have antibody to blood group A in their serum. Group O Individuals have antibodies to both red cells of blood group A and blood group B. If ABO incompatible blood is administered there may be an immediate and fatal transfusion reaction mediated by these naturally-occurring antibodies.

In ABO blood grouping the antigens present on the red cells are typed (the forward group), at RNSH this is in tubes for the primary group and in cards for the check group.

When primary grouping in tubes is carried out testing for antibody in serum (the reverse group) is also carried out. These are carbohydrate antigens.

THE Rh SYSTEM

The terms Rh positive and negative refer to the presence or absence of the Rh(D) antigen. The Rh(D) antigen is the most immunogenic blood group protein and antibodies to the D antigen are commonly detected in pretransfusion testing in Caucasians. Rh incompatibility between mother and foetus is a common cause of haemolytic disease of the newborn in Caucasians.

The Rh(D) antigen is coded by the RH D gene, in Rh negative individuals the D gene is absent. The CcEe antigens are carried on a protein of identical structure to the Rh(D) protein coded by one of four alleles at the RH CE locus (Ce, cE, CE or ce). The RhCE locus is next to the D locus on chromosome 1.

For the Rh System, International Society for Blood Transfusion recognises both Fisher-Race terminology, in which single letters are used to denote antigens, and a numerical system, in which the Rh system is 004, with a three digit number denoting the antigen.

Fisher-Race Antigen	ISBT Number
D	004001
C	004002
E	004003
c	004004
e	004005

A shorthand terminology is also used:
R1 for Ce with D, and R2 for cE with D, r for ce in the absence of D, Rh(D) typing tests are performed on all patients and donors to establish their status as Rh (D) positive or negative.

GEL CARD TECHNOLOGY

Principle
Antibodies that react with red cell antigens coat the red cell and sometimes agglutination results. When antibody-coated red cells are added to an anti-human globulin solution the antibodies in this solution react with the antbody on the red cells and agglutination results. When agglutinates are centrifuged through gel the rate of travel through the column is proportional to the size of the agglutinates.

In the DiaMed system for typing red cells are spun into a column containing antiserum to the red cell antigens. For screening, the patient's serum and reagent red cells are placed in the reaction chamber above the column. Upon centrifugation, the red cells are exposed to the antiglobulin reagent and agglutinated cells are trapped. Non-agglutinated cells are not impeded form a button at the base of the column.

The difference in specific gravity between the red cells and serum results in the red cells to passing into the column while the serum is excluded (less dense). This eliminates the wash step traditionally required when the antiglobulin test is carried out in tubes. The polymers in the diluent as in addition to excluding the serum also enhance agglutination.

Advantages of Gel Card Technology include:

Standardisation of procedure

Less subjectivity in interpretation

Simplification of testing

Increased safety

GROUPING WITH DIAMED GEL CARDS

Principle
The cards containing specific typing reagents (monoclonal antibodies to the various red cell antigens).

- 0.8% v/v suspension of Patient's cells
- Micropipette
- DiaMed system Centrifuge
- Disposable pipette tips

Procedure

1. Label the cassette with the patient's name or first 3 letters.
2. Add cells
3. Centrifuge the cassette using the DiaMed centrifuge.
4. Read the front and back of the individual columns for agglutination.
5. Record results in the computer system and on the request form.

Interpretation of Results

- A positive reaction {score 3 (1+w); 5 (1+); 8 (2+); 10 (3+); 12 (4+)} is recorded when red cells are retained in or above the gel column after centrifugation. A negative reaction is recorded (as 0) when a distinct button of cells sediment to the bottom of the column after centrifugation.

- Haemolysis is recorded as a positive reaction. Reading and interpretation of results is done only on initial spin and performed within 30 minutes of centrifugation.

- If the cells agglutinate with the anti-A only, Group A, with anti-B only Group B, with both anti-A and anti-B, Group AB and if there is no agglutination with anti-A and anti-B the patient is group O.

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Left, Group O Rh+ ; Right, Group A Rh-	Left, Group B Rh+ ; Right, Group AB Rh-