Four monoclonal anti-human Tg antibodies, selected for their specificity, affinity and complementarity, are coated onto the solid phase (coated tubes). A fifth monoclonal antibody, labeled with Iodine 125 and recognizing a different epitope from those recognized by the 4 adsorbed monoclonals, is used as the tracer. The monoclonals target epitopic zones unrecognized by the majority of circulating anti-Tg auto-antibodies. The functional sensitivity level of 0.7 ng/ml enables the detection of residues or of recurrences as early as possible. The two-step technique means that the hook effect only comes in at 800 000 ng/mL. These features make the kit Cisbio THYRO a robust and reliable assay.