Methods and devices for determining the concentration of at least one analyte in a body fluid

A determination method of determining a color expectation range for assessing the plausibility of an assumed reaction time value used in an analytical measurement based on a color formation reaction, the method comprising:

• a) providing a training set of optical test strips each having a reagent test region;
• b) providing a training set of body fluid samples and applying at least one of the samples to the reagent test region of each optical test strip;
• c) capturing, by a mobile device having a camera, a training set of images, comprising:
• a first training subset of images comprising images of at least one part of at least some of the reagent test regions of the training set of optical test strips having the sample of body fluid applied thereto captured at in-time capture time values, the capture time value referring to the time that has passed between the application of the sample in step b) and the capturing of the image;
• a second training subset of images comprising images of at least one part of at least some of the reagent test regions of the training set of optical test strips having the sample of body fluid applied thereto captured at delayed capture time values;
• d) determining a training set of color formation values from the images of the training set of images, the training set of color formation values comprising color formation values of a color channel for the color formation of the reagent test region of the optical test strips of the training set of optical test strips for in-time capture time values and for delayed capture time values;
• and
• e) deriving the color expectation range for the color channel from the training set of color formation values, the color expectation range defining an expected range of color formation values for in-time capture time values and tolerably delayed capture time values, wherein for the tolerably delayed capture time values the delay does not exceed at least one predefined expiry threshold dmax.