 The equipment needed is usually less complicated and can be used in the field.The following table lists the enzymatic markers commonly used in ELISA assays, which allow the results of the assay to be measured upon completion.Because the ELISA can be performed to evaluate either the presence of antigen or the presence of antibody in a sample, it is a useful tool for determining serum antibody concentrations (such as with the HIV test or West Nile virus).