System for withdrawing blood

System for withdrawing body fluid, comprising a drive unit (100, 100 ') is moved to execute a lancing process from a resting position into a lancing position with a plunger (10, 110), and a lancing unit (20, 120, 120'), in which a lancet (30, 130, 130 ') is with a needle, which is arranged in the rest position of the plunger within the lancing unit and is displaced by the plunger during movement in the puncturing position so that the needle is at least partially by a outlet opening (41, 41 ') emerges into the lancing unit, said plunger and lancet for carrying out the lancing process are coupled together by a form fit. Furthermore, the application relates to a method for temporarily extending a needle from a device for withdrawing body fluid, and a lancing unit for attachment to a drive unit.