Method for the quantitative determination of a free form of substances present in biological fluids

摘要

Disclosed is a method for the direct determination of the free fraction of analytes present in biological fluids in a free form and in a form bound to one or more endogenous ligands (said free and bound forms being in equilibrium with one another). This method provides for a (preferably substantially simultaneous) use:a first ligand L1 capable of sequestering an analyte quantity proportionate to the free-analyte concentration present in a biological fluid and to subsequently release it, after removal from the biological fluid of the specific endogenous ligand, as a result of the addition of an appropriate selective dissociating agent; a second ligand capable of binding both the previously released analyte and a labelled version of the analyte, even in the presence of the dissociating agent; a selective dissociating agent; and a quantity of labelled analyte. The measured level of the labelled analyte which binds to the second exogenous ligand (or which remains unbound) is used to determine the concentration of the free analyte in the fluid.