Both the presence of antigen or antibodies can be measured, for instance in the detection of infection, the presence of antibody against the pathogen is measured, and for measuring hormones such as insulin, the insulin acts as the antigen.
Both the presence of antigen or antibodies can be measured. The presence of antibody against the pathogen is measured. This was for instance in the detection of infection. The insulin is measuring hormones such as insulin. The insulin acts as the antigen.