What reaction occurs between the antigen and the antibody in the VDRL test?

In the VDRL test, the primary reaction that occurs between the antigen and the antibody is flocculation. This test is a non-treponemal test used for screening syphilis, where a cardiolipin antigen is mixed with the patient's serum. If antibodies against the cardiolipin are present, a visible agglutination, or flocculation, occurs as a result of the interaction between the antigen and the antibodies.

Flocculation is characterized by the formation of visible clumps or flakes, which indicates a positive reaction. In this context, flocculation is a distinguishing feature because it contrasts with the more soluble reactions seen in precipitation assays or the cellular lysis seen in hemolysis reactions. Understanding the specific nature of this reaction is critical for correctly interpreting the results of the VDRL test and differentiating it from other types of immunological reactions.