The Competition/Inhibition ELISA approaches the problem of measuring the concentration of an analyte in a sample from the opposite direction of any other version of the assay. First, a known antigen is used to coat the microplate sample wells. Secondly, the test sample material is added, and lastly the enzyme-labeled antibody is introduced that allows detection of results. Since the test analyte is ‘competing’ to bind with the enzyme-labeled antibody, the presence of the analyte will decrease the signal output commensurate with its concentration. This inverted approach also allows for testing of an unknown sample without need for purification, and is applicable to a wide range of experiments. The complexity and difficulty of this technique is similar to the Indirect or Sandwich ELISA protocols in regards to time and expense.