A measuring system for determining blood glucose includes a photometric measuring unit with a light source and a detector, and an analytical test element, to which a body fluid sample can be applied, and which can be placed in a beam path between the light source and the detector for optical detection of an analyte. For an improved multi-wavelength measurement, it is proposed that the light source includes a first emitter that can be actuated in a first wavelength range to emit pulsating alternating light and a second emitter that can be excited in a second wavelength range to emit fluorescent light.