Certain laboratory tests are available to detect the presence of antibodies in an individual. These laboratory tests are commonly used in diagnostic procedures because the presence of a certain antibody indicates the presence of a certain disease. The study of serum for its antibody content is known as serology.
One of the objects of serology is to determine the titer of antibody present in the individual. The titer is an estimate of the antibody level in a unit volume of serum. It is determined as a reactive dilution of the serum and is usually expressed in a ratio such as 1:100.
The agglutination and precipitation tests. Serological tests that involve clumping of an antigen are called agglutination tests. Antibodies involved in agglutination tests are called agglutinins. When the antibody molecules unite with antigen molecules on the surface of bacteria, red blood cells, or particles, they cause the cells to stick together and form large clumps (Figure 1 ).