Figure 1 Automated chemiluminescence system using a two‐site sandwich immunoassay. (A) Normal assay showing radiolabelled sandwiches containing thyroid‐stimulating hormone (TSH), which sediment in a magnetic field. (B) Assay showing interference of human anti‐mouse antibodies by creating a radiolabelled sandwich. (C) Prevention of interference: adding immunoglobulin (Ig) G forms unlabelled sandwiches, which are not detected by the assay. Fl, fluorescein‐labelled anti‐TSH sheep monoclonal antibodies. I*, I‐125‐labelled anti‐TSH mouse monoclonal antibodies. Some clipart used with permission from Madlantern Arts.