Phlebotomists are trained to avoid or minimize the practice of "fishing" or probing for a vein if the initial attempt to insert the collection needle into a vein is unsuccessful. In addition to the probing process being painful to the patient, it could cause tissue and vascular damage at and around the phlebotomy site. The underlying damaged tissues release chemicals called cytokines along with blood that may pool in the surrounding tissue. This may be drawn into the vacuum of the collection tube resulting in a fluid that is not truly representative of the circulating blood. Such mixtures of vascular blood and tissue fluids are also more likely to be hemolyzed.
