Sodium fluoride is the most commonly used preservative in blood samples for alcohol estimation because it acts as a glycolysis inhibitor. This prevents the breakdown of glucose by red blood cells after sample collection, which otherwise can lead to a false decrease in blood alcohol concentration. Additionally, sodium fluoride has antimicrobial properties that help preserve the integrity of the sample during transport and storage. Other anticoagulants like EDTA, heparin, or potassium oxalate do not inhibit glycolysis effectively and thus are less reliable for accurate alcohol estimation.

Reference: Harrison’s Principles of Internal Medicine, J. Larry Jameson, 21st Edition.