A method of determining a concentration of an analyte in a bodily fluid, the method comprising using a mobile device having a camera , wherein the method comprises capturing at least one image of at least a part of an optical test strip having a test field by using the camera , and wherein the method further comprises determining at least one analyte concentration value from color formation of the test field , wherein the method comprises: i) providing, in the mobile device , at least one correlation for transforming color formation of the test field into the analyte concentration value, wherein the term "correlation" refers to a predetermined or determinable relationship between information derived from the at least one image and at least one analytical measurement concentration value, wherein the correlation is determined by using empirical or semi-empirical methods, also referred to as a training, wherein the training comprises the use of one or more artificial neural network, wherein the training comprises performing a plurality of measurements transforming the color formation into analyte concentration values by using at least one color reference card ; ii) providing, in the mobile device , at least one item of clearance information, the at least one item of clearance information indicating a level of confidence for the correlation; and iii) if the item of clearance information indicates a sufficient level of confidence for the correlation, providing, by the mobile device , indication to a user that the capturing of the at least one image does not require using a color reference card ; and iv) if the item of clearance information indicates an insufficient level of confidence for the correlation, providing, by the mobile device , indication to a user that the capturing of the at least one image requires capturing of at least one image of at least one color reference card , wherein using the at least one reference card generates reference card measurement data used for training of the at least one artificial neural network. i) providing, in the mobile device , at least one correlation for transforming color formation of the test field into the analyte concentration value, wherein the term "correlation" refers to a predetermined or determinable relationship between information derived from the at least one image and at least one analytical measurement concentration value, wherein the correlation is determined by using empirical or semi-empirical methods, also referred to as a training, wherein the training comprises the use of one or more artificial neural network, wherein the training comprises performing a plurality of measurements transforming the color formation into analyte concentration values by using at least one color reference card ; ii) providing, in the mobile device , at least one item of clearance information, the at least one item of clearance information indicating a level of confidence for the correlation; and iii) if the item of clearance information indicates a sufficient level of confidence for the correlation, providing, by the mobile device , indication to a user that the capturing of the at least one image does not require using a color reference card ; and iv) if the item of clearance information indicates an insufficient level of confidence for the correlation, providing, by the mobile device , indication to a user that the capturing of the at least one image requires capturing of at least one image of at least one color reference card , wherein using the at least one reference card generates reference card measurement data used for training of the at least one artificial neural network. <EOS>