What blood tube must be used when testing blood glucose externally?

• A. Plain red
• B. Sodium citrate (blue)
• C. EDTA (purple)
• D. Fluoride oxalate (yellow)

Answer: (D)

The key idea is preserving the glucose level from the moment the blood is drawn. Glucose in a blood sample can be consumed by cells and enzymes (glycolysis) after collection, which lowers the measured glucose if no inhibitors are present. A fluoride oxalate tube provides two things at once: a glycolysis inhibitor (sodium fluoride) that stops the breakdown of glucose, and an anticoagulant (oxalate) that prevents clotting. This combination keeps the glucose concentration stable for accurate external testing.

Plain red has no additive to stop glycolysis, so glucose can drop. Sodium citrate is used for coagulation tests and doesn’t stop glycolysis. EDTA prevents coagulation for hematology tests but doesn’t inhibit glycolysis. Therefore, the fluoride oxalate tube is the appropriate choice for reliable glucose measurement.