Which statement correctly describes gray top tubes and their use?

• A. Gray Top Tubes Contain Potassium Oxalate With Sodium Fluoride And Are Used For Glucose Testing.
• B. Gray Top Tubes Contain Heparin.
• C. Gray Top Tubes Contain EDTA.
• D. Gray Top Tubes Are Used For CBC.

Answer: (A)

Gray-top tubes are designed to preserve blood glucose levels by combining an anticoagulant with a glycolysis inhibitor. The potassium oxalate acts as an anticoagulant by binding calcium, preventing the blood from clotting. The sodium fluoride slows down glycolysis, which would otherwise reduce the measured glucose concentration after the blood is drawn. Together, this makes gray-top tubes ideal for accurate glucose testing.

These tubes aren’t used for complete blood counts because CBC requires an EDTA-containing tube (purple) to preserve cells and provide reliable cell counts, not oxalate with fluoride. They also don’t contain heparin (green-top tubes) and aren’t the standard choice for CBC or blood cell morphology.