Which color-top tube is used for glucose testing in this system?

• A. Grey
• B. Blue
• C. Yellow
• D. Green

Answer: (A)

Glucose testing needs a blood sample whose glucose level stays stable until analysis. The grey-top tube contains sodium fluoride, a glycolysis inhibitor, along with potassium oxalate as an anticoagulant. The fluoride slows down the red blood cells’ consumption of glucose, preventing glycolysis from lowering the glucose level before testing. That preservation is essential for an accurate measurement.

Other color-top tubes use different additives that don’t protect glucose in the same way. Blue-top tubes have citrate for coagulation studies, yellow-top tubes are for culture or certain specialty additives, and green-top tubes use heparin for general chemistry—none provide the glycolysis inhibition needed for reliable glucose results. Hence, the grey-top tube is used for glucose testing.