Which is the best anticoagulant to send sample for serum electrolyte measurement?

EDTA- it is an anticoagulant that is preferred when we want to look at the morphology or we want to do any of the blood counts. Sodium fluoride - it inhibits enolase enzyme thus inhibits glycolysis process , so it is used for glucose estimation . Citrate - 3.2%Trisodium citrate - it is used for the determining the value of ESR and is also used for doing any kind of coagulation study. All the three (sodium EDTA, sodium fluoride, trisodium citrate) above use sodium. therefore, if we use any of these chemicals for the purpose of Serum Electrolyte measurement, the value of sodium and other electrolytes are going to be altered. So WHO recommends that for the purpose of Serum Electrolyte measurement we use an anticoagulant Lithium Heparin. It doesn't cause any alterations in the serum electrolytes.