A method for evaluating the quality of an analysis element which is useful for determining the concentration of an analyte in a liquid sample, comprising: (a) providing an analysis element in which a reagent system is operatively integrated, wherein the reagent system contains at least one enzyme and at least one co-enzyme, wherein a reaction of the sample with the reagent system includes a complex formation of at least the enzyme and the co-enzyme, and wherein a chemically modified form of the co-enzyme is a fluorophore; (b) reacting the sample with the reagent system in order to produce a change of the quantity and/or of the luminescence properties of the fluorophore, wherein the quantity and/or the luminescence properties of the fluorophore relate to the concentration of the analyte; (c) optionally measuring a first measurement variable; (c') measuring at least a second measurement variable, wherein the first and the second measurement variable are characteristic for the quantity of the fluorophore and/or for the degree of complexation of the fluorophore, and wherein the second measurement variable is the fluorescence lifetime of the fluorophore; (d) optionally determining a first concentration c1 initial of the fluorophore and/or of the analyte on the basis of the first measurement variable, using a pre-set enzyme activity A Enz (preset); (e) determining a second concentration c2 ref of the fluorophore and/or of the analyte on the basis of the second measurement variable, using the pre-set enzyme activity A Enz (preset); and/or determining the measured enzyme activity A Enz (measured) on the basis of the second measurement variable and taking into account either the first concentration c1 initial from step (d) or a known concentration c1 known of the analyte in the sample; and (f) evaluating the quality of the analysis element using an evaluation algorithm, wherein the evaluation algorithm comprises obtaining information relating to the measured enzyme activity A Enz (measured), wherein said information is at least partly derived from the measurement of the fluorescence lifetime of the fluorophore, either directly by determining the measured enzyme activity A Enz (measured) according to step (e), or indirectly by comparing the second concentration c2 ref to the first concentration c1 initial. (a) providing an analysis element in which a reagent system is operatively integrated, wherein the reagent system contains at least one enzyme and at least one co-enzyme, wherein a reaction of the sample with the reagent system includes a complex formation of at least the enzyme and the co-enzyme, and wherein a chemically modified form of the co-enzyme is a fluorophore; (b) reacting the sample with the reagent system in order to produce a change of the quantity and/or of the luminescence properties of the fluorophore, wherein the quantity and/or the luminescence properties of the fluorophore relate to the concentration of the analyte; (c) optionally measuring a first measurement variable; (c') measuring at least a second measurement variable, wherein the first and the second measurement variable are characteristic for the quantity of the fluorophore and/or for the degree of complexation of the fluorophore, and wherein the second measurement variable is the fluorescence lifetime of the fluorophore; (d) optionally determining a first concentration c1 initial of the fluorophore and/or of the analyte on the basis of the first measurement variable, using a pre-set enzyme activity A Enz (preset); (e) determining a second concentration c2 ref of the fluorophore and/or of the analyte on the basis of the second measurement variable, using the pre-set enzyme activity A Enz (preset); and/or determining the measured enzyme activity A Enz (measured) on the basis of the second measurement variable and taking into account either the first concentration c1 initial from step (d) or a known concentration c1 known of the analyte in the sample; and (f) evaluating the quality of the analysis element using an evaluation algorithm, wherein the evaluation algorithm comprises obtaining information relating to the measured enzyme activity A Enz (measured), wherein said information is at least partly derived from the measurement of the fluorescence lifetime of the fluorophore, either directly by determining the measured enzyme activity A Enz (measured) according to step (e), or indirectly by comparing the second concentration c2 ref to the first concentration c1 initial.