Which color top contains sodium fluoride for glycolysis inhibition?

• A. Red
• B. Gray
• C. Light Blue
• D. Gold

Answer: (B)

Glycolysis inhibition in glucose testing relies on a fluoride-containing tube. The color that signals this additive is gray. In gray top tubes, sodium fluoride acts as the antiglycolytic agent, inhibiting the glycolytic enzymes and preventing glucose from being consumed by cells after collection. This helps preserve the glucose level until analysis. The gray tube also contains an anticoagulant (potassium oxalate), so blood doesn’t clot and you can use the sample for plasma glucose measurements. Other colored tubes are designed for different tests and have different additives, so they don’t provide the fluoride-based protection against glycolysis.