Which additive is commonly used to prevent glycolysis in samples for glucose testing?

• A. Sodium fluoride
• B. Heparin
• C. EDTA
• D. Citrate

Answer: (A)

Glycolysis continues in a collected blood sample, so glucose levels can fall before you measure them. Sodium fluoride is the additive used to prevent this by inhibiting enolase, a late step in the glycolytic pathway. This slows or stops the conversion of glucose into downstream metabolites, helping preserve the true glucose concentration for testing. That’s why fluoride is used in gray-top tubes (often with potassium oxalate as an anticoagulant) for glucose measurements. Other common additives like heparin, EDTA, or citrate mainly serve to prevent clotting or preserve other aspects of the sample; they don’t inhibit glycolysis, so they don’t reliably preserve glucose levels. Keep in mind fluoride’s effect isn’t instantaneous, so prompt processing or cooling improves accuracy.