Some of the main diagnostic reagents and kits include antigen antibody reaction kit. These kits are designed to determine the presence of a certain pathogen in the blood. Thus, an antigen antibody reaction is used. The antigen generated by the pathogen exists in the blood of the host. An antibody to that specific antigen is provided in the kit. Antigen-antibody reactions are used even in ABO blood typing. Here, antibodies against the three blood antigens are used to determine the blood group of a given sample. Diagnostic kits are designed for the rapid testing and identification of diseases. The diagnostic kits contain solutions and reagents which support a set number of reactions. They are highly specific and reliable.