What additive is found in the gray tube top, used for glucose testing?

The correct answer for the additive found in the gray tube top used for glucose testing is potassium oxalate and sodium fluoride.

This combination serves a specific purpose in the collection and preservation of glucose samples. Potassium oxalate acts as an anticoagulant, preventing blood from clotting, which is crucial in ensuring accurate measurement of glucose levels. Sodium fluoride, on the other hand, is a glycolytic inhibitor that prevents the breakdown of glucose by cellular metabolism. This is particularly important as it preserves the glucose concentration in the sample, allowing for reliable testing results.

In glucose testing, it's vital to maintain the integrity of the sample. The gray tube's specific additives ensure that glucose does not degrade prior to analysis, leading to more accurate outcomes for patient assessment. This is why the combination of potassium oxalate and sodium fluoride is standard for this type of testing, unlike the other options that include different anticoagulants or additives not specifically suited for glucose preservation and measurement.