The invention relates to an indwelling catheter in particular an intravenous indwelling catheter for emergency treatment. The catheter comprises a housing and a puncturing cannula, which can be introduced into and removed from the housing interior in the longitudinal direction of the housing and which extends through a front housing opening, in such a way that when the cannula is fully introduced, an entry opening is located outside the housing. A collection component stores a blood sample, the component being held in a displaceable manner on the housing with the aid of a fixing element and being displaced between a coupled position, in which a self-filling reservoir, which is configured in the collection component, is in contact with an exit opening of the cannula in order to receive a sample of blood that traverses the cannula and an uncoupled position, in which the reservoir is separated from the exit opening of the cannula and the collection component is held on the housing by the fixing element.