Which of the following is an example of precipitation reaction?
Widal Test
Coomb's Test
Counter Current immunoelectrophoresis
Weil-Felix Test
Precipitation is a method for detecting an antigen-antibody reaction. When antigen and antibody combine in the proper propoions, a visible precipitate is formed. Optimum antigen-antibody ratios can be produced by allowing one to diffuse into the other, most commonly through an agar matrix (immunodiffusion). Counterimmunoelectrophoresis (CIE) is a type of precipitation reaction where immunodiffusion carried out in an electrophoretic field. Both the speed and the sensitivity of immunodiffusion are improved by CIE. Ref: Ray C.G., Ryan K.J. (2010). Chapter 4. Principles of Laboratory Diagnosis of Infectious Diseases. In C.G. Ray, K.J. Ryan (Eds), Sherris Medical Microbiology, 5e.