This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: AIIMS 2017, Subject name: Pathology
Which is the best anticoagulant to send sample for serum electrolyte measurement? 
Select and explain. 
A. EDTA, B. Lithium heparin, C. Sodium fluoride, D. Citrate
B: Lithium heparin
Answer: B: Lithium heparin 
Explanation: 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.