Which of the following is the most appropriate specimen for glucose analysis when glycolysis must be inhibited?

• A. EDTA plasma
• B. Fluoride oxalate plasma
• C. Heparinized plasma
• D. Serum

Answer: (B)

Glycolysis continues in blood samples after collection, which lowers the measured glucose unless glycolysis is inhibited. The best specimen for accurate glucose analysis is fluoride oxalate plasma because sodium fluoride inhibits glycolysis by blocking enolase, and oxalate acts as an anticoagulant to keep the sample as plasma rather than allowing it to clot. This combination stabilizes the glucose level for reliable measurement, typically using a gray-top tube.

Other options lack glycolysis inhibition. EDTA plasma and heparinized plasma prevent clotting but do not stop glycolysis, so glucose can still drop before analysis. Serum forms after clotting, and glycolysis continues during clot formation, also leading to lower glucose values.