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 anti-body 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 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.Column gel card The polymers in the diluent as in addition to excluding the serum also enhance agglutination. 

      Advantages of Gel Card Technology include:
      1.Standardisation of procedure
      2.Less subjectivity in interpretation
      3.Simplification of testing
      4.Increased safety