Abstract: Method for the determination of an analyte in a volume of a fluid sample, in particular of anti-TSH receptor autoantibodies in a patient serum, in which one or more determination reagent(s) which contains or which containa) a predetermined amount of a binder (B) for the analyte (A) andb) a predetermined amount of a competitor (K) which is likewise bound by the binder (B), in such a way that the extent of its binding to the binder (B) is correlated with the simultaneous presence of the analyte (A) and/or its amount in the sample, the competitor (K) being labelled, or being capable of being labelled, with a label which permits its qualitative and/or quantitative determination, is or are added to the sample with the formation of a liquid reaction mixture, whereinc) the liquid reaction mixture is reacted simultaneously or subsequently with a solid phase to which a substance (Imm) for the selective immobilization of the amount of competitor (K) not bound to the binder (B) is bound, and optionally with a labelled r

Abstract: A method is revealed for the quantitative determination of the proportion of the free form of a thyroid hormone ligand in a sample of a biological fluid in which the ligand is present partly in the free form and also partly in a form in which it is bound to physiological binding proteins. In the first step, a ligand derivative of the thyroid hormone with an immunoglobulin, a labelled specific binder, and a test tube whose walls are coated with an excess of a protein material are provided. In the second step, a sample of the biological fluid containing an unknown amount of the free thyroid hormone ligand, a solution containing a known amount of the ligand derivative, and a solution containing a known, less than stoichiometric amount of the labelled specific binder are added to the test tube to form a liquid reaction mixture.