Two linked reactions form the basis of this type of test- the capture by the antibody of an enzyme labeled dioxin fragment and the inhibition of that capture by analyte molecules in the sample.

The baseline binding of the dioxin-enzyme conjugate to the antibody is affected by both concentration and crossreactivity of analyte. When dioxin-specific binding sites on the antibody are occupied by analyte molecules, fewer sites are available to capture the dioxin-enzyme conjugate.

Crossreactivity, the ability of an analyte molecule to bind to the antibody, decreases as the structural similarity to the target analyte decreases.

Key concept: test response is by competitive inhibition and is strongest for analyte structures which are most similar to the target.