The present invention relates to a method for determining an organ function in a subject, comprising the steps of: providing a first concentration-time curve obtained by transcutaneously measuring in a body fluid at a first position background fluorescence in at least one first time point and fluorescence of an indicator compound in at least a second, a third, a fourth, a fifth, and a sixth time point; providing a second concentration curve obtained by transcutaneously measuring in a body fluid at a second position background fluorescence in at least one seventh time point and fluorescence of an indicator compound in at least a eighth, a ninth, a tenth, an eleventh, and a twelfth time point; fitting the first and the second concentration curve into a kinetic model representing at least four diffusion compartments; and thereby determining an organ function in a subject. The invention further relates to a device for determining an organ function according to the method of the present invention, said device comprising a first sensor for transcutaneously measuring fluorescence of an indicator at a first position, a second sensor for transcutaneously measuring fluorescence of an indicator at a second position; and a data processing unit for fitting the values obtained by the sensors into a kinetic model of one of the preceding claims. The present invention also relates to a kit comprising a device of the present invention and an indicator compound, as well as to a computer or computer network comprising at least one processor, wherein the computer or computer network is adapted to perform the method according to the present invention.