VERFAHREN UND TESTKIT ZUR BESTIMMUNG FREIER WIRKSTOFFE IN BIOLOGISCHEN FLUESSIGKEITEN

Method for the determination of the concentration of the free component of an active agent present in a biological liquid in the presence of natural binders, the free and the bound component of the active agent being in equilibrium with each other. The method comprises a) bringing a sample of the liquid into contact with an unlabelled antibody; b) separating the sample from the unlabelled antibody; c) incubating the unlabelled antibody with a labelled substance (tracer) which cross-reacts with it; d) measuring the proportion of the tracer which is bound or not bound to the antibody and calculating the concentration of the free component of the active agent therefrom, the amount of the unlabelled antibody and/or its affinity for the active agent being so small that they do not substantially affect the equilibrium between the free and bound component of the active substance, the tracer having an appreciably higher or an appreciably lower affinity for the antibody and for the active agent itself, and a test kit suitable for this method.