The unit (20) has a piercing element formed from sheet metal plate in a single piece and inserted into skin of user. An analytical detecting element (24) is supplied with body fluid obtained from the skin. The detecting element has reagents reacting with analyte in the body fluid, and transparent carrier plates laminated with the reagents. The carrier plates form an optical interface in a contact surface for photometric measurement value detection, where the contact surface is turned away from the reagents. The optical interface is provided with device sided optical adaptor (68). An independent claim is also included for a testing system including an optical measurement device. Two LEDs are arranged over a light conductor.
