Determining at least one concentration of at least one analyte in a sample (110), preferably at least one metabolite in a sample of a body fluid, comprises e.g.: using at least one test element (50) with at least one test chemical (102) and determining at least one reaction of the test chemical with the analyte； further using at least one marker (104) that is different from the analyte and determining at least one diffusion of the marker in the sample or at least one portion of the sample； and determining the concentration of the analyte from the reaction of the test chemical with the analyte. Determining at least one concentration of at least one analyte in a sample (110), preferably at least one metabolite in a sample of a body fluid, comprises using at least one test element (50) with at least one test chemical (102), determining at least one reaction of the test chemical with the analyte, further using at least one marker (104) that is different from the analyte, determining at least one diffusion of the marker in the sample or at least one portion of the sample, generating at least one correction information from the diffusion of the marker, and determining the concentration of the analyte from the reaction of the test chemical with the analyte considering the correction information. Independent claims are also included for: (1) test element useful in the above method, comprising (i) at least one test chemical to carry out at least one detectable reaction with the analyte, (ii) at least one marker in at least one first area of the test element, to diffuse at least partially from the first region of the test element into at least one second region； and (2) an apparatus for the above method, comprising (a) at least one test element with at least one test chemical, and (b) at least one marker, where the apparatus is adapted for determining at least one reaction of the test chemical with the analyte, determining at least one diffusion of the marker in the sample or
