The hemagglutination reaction used to determine blood group (A, B, O) is a qualitative test; that is, it simply shows whether antibodies are present or not [View].

However, such tests can be made semiquantitative; that is, provide a number representing the approximate concentration of antibodies in the serum being tested.

The most common procedure is to add a fixed amount of particles (e.g., red blood cells) carrying antigen on their surface to a series of tubes containing increasing (usually doubling) dilutions of the antiserum. The titer of the antiserum is the reciprocal of the highest dilution in which agglutination occurs.

An example: Passive Hemagglutination

In passive hemagglutination, red blood cells are agglutinated by antibodies directed against antigens that have been coupled chemically to the red cell surface. Thus the red cell now serves simply as a easily visible indicator of an antigen-antibody interaction.

In the example shown here, the wells in the

top row

contains serial dilutions of a human serum mixed with a constant number of human red cells that have been coated with human thyroglobulin. The reaction is strongly positive in the first 5 wells — the bottom of each of these wells is covered with a sheet of agglutinated red cells. Wells 6–9 show increasingly weak reactions.

bottom row

contains the same patient's serum mixed with normal, uncoated red cells and thus serve as a control to be sure that the results in the top row are caused by anti-thyroglobulin antibodies and not antibodies against normal proteins on the red cell surface.

middle row

contains normal human serum with thyroglobulin-coated red cells — another control.

Anti-thyroglobulin antibodies are often found in patients with such thyroid disorders as myxedema and Graves' disease

The photograph is courtesy of Dr. C. Lynne Burek.

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12 May 2011