A blood transfusion is the transfer of blood or blood components from one lifeform to another. Compatibility issues between the blood donor and recipient can occur due to differences in antigens or antibodies, specialized proteins used to fight foreign bodies such as viruses or bacteria. It is also likely that interspecies incompatibilities would occur due to more fundamental differences in blood chemistry; for example, Human hemoglobin is iron-based, whereas Vulcan hemoglobin is copper-based.
Bolians are unable to accept direct transfusions from Vulcans; doing so would result in the death of the Bolian. However, there have been instances where incompatible blood was altered in order to make a transfusion possible. (VOY: "Prototype")
A transfusion from Spock once saved Sarek's life. (TOS: "Journey to Babel")
A Kazon retrieved by the USS Voyager required a complete blood transfusion after his blood cells had bonded with metalic nuclei. (VOY: "State of Flux")
Shinzon wanted to capture Captain Jean-Luc Picard because a complete transfusion of Picard's blood was necessary for Shinzon to survive. (Star Trek Nemesis)