This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: miscellaneous, Subject name: Pathology
If you are in PHC, which anticoagulant is used to sent the blood sample for blood glucose estimation? - 
Select and explain. 
A. EDTA, B. Heparin, C. Potassium oxalate, D. Potassium oxalate + sodium fluoride
D: Potassium oxalate + sodium fluoride
Answer: D: Potassium oxalate + sodium fluoride 
Explanation: It is used when blood is collected for glucose estimations. It is a weak anticoagulant but is often added as a preservative for blood glucose together with potassium oxalate as an anticoagulant. It is effective at a concentration of 2mg/ml blood. It inhibits the enzyme enolase (sodium fluoride) thus inhibiting glycolysis. Na fluoride/K oxalates are mixed in the ratio 1:3.