Test method and test device for analysing a body fluid

A method of detecting reagent layer failure on a test tape having a plurality of test fields, the method comprising the steps of:

• providing an unused test field of the test tape to initiate a test, wherein the test tape is in a test device having a measuring unit comprising at least one radiation source to generate at least one wavelength of light and a photodiode for reflection-photometric signal detection of the at least one wavelength of light;
• photometrically scanning the unused test field with the measuring unit and detecting relative remission measurement signals of the at least one wavelength of light generated by the at least one radiation source over a duration of a waiting time prior to applying a body fluid sample to the unused test field;
• calculating a control value based upon a blank measurement signal difference between relative remissions detected at a beginning and at an end of the waiting time;
• and
• detecting a reagent layer failure and discarding the test if the control value is above zero and below a preset threshold.