If a sample is to be used for plasma glucose testing, which tube is most appropriate?

• A. Fluoride-oxalate tubes
• B. EDTA tubes
• C. Heparin tubes
• D. Red-top tubes

Answer: (A)

Glucose levels in drawn blood continue to drop as cells keep metabolizing sugar after collection. To get an accurate plasma glucose reading, you need a tube that both prevents clotting and stops glycolysis. The fluoride in fluoride-oxalate tubes inhibits glycolytic enzymes, while oxalate acts as an anticoagulant. This combination keeps the glucose level stable from collection to analysis, so the result reflects the true plasma glucose.

Other tubes lack a glycolysis inhibitor. EDTA and heparin tubes will anticoagulate but don’t stop glycolysis, so glucose can decrease if there’s any delay before processing. Red-top tubes (serum) also don’t include a glycolysis inhibitor, and glucose can fall during clotting and handling. Therefore, the fluoride-oxalate tube is the best choice for reliable plasma glucose testing.