<prompt> Which vacutainer is used for electrolyte estimation?Na CitrateEDTAFluorideLithium heparin  <response>: Ans. d Lithium heparinRef: Henry Clinical chemistryHeparin, a mucoitin polysulfuric acid, is an effective anticoagulant available as lithium heparin LiHep and sodium heparin NaHep in green-top tubes. Heparin accelerates the action of antithrombin III, neutralizing thrombin and preventing the formation of fibrin. Heparin has an advantage over EDTA as an anticoagulant, as it does not affect levels of ions such as calcium. However, heparin can interfere with some immunoassays. Heparin should not be used for coagulation or hematology testing. 