| abstract |
A method of measuring the concentration of a free ligand in a biological fluid containing the free ligand and ligand bound to endogenous binding agent, comprises; a) mixing a sample of the fluid with an analogue of the ligand, a specific binder with which the free ligand and the ligand analogue bind, and an exogenous binding agent which binds the ligand analogue but not the ligand, either the ligand analogue or the specific binder being labelled; b) incubating the resulting mixture so that the ligand and ligand analogue compete for the specific binder; c) determining either the amount of the labelled analogue bound to the specific binder or the exogenous binding agent or the amount of labelled specific binder bound, or not bound, to the ligand analogue; and d) correlating the determined amount to the amount of free ligand present in the sample. The method is especially usefull where the ligand analogue binds with endogenous binding agent and the extent of binding varies from sample to sample of the biological fluid. It may be used to measure concentration of free thyroid hormones and other hormones in body fluids, employing antibodies specific to the ligand analogue as the exogenous binding agents. |