What is the primary reason for using the gray tube for glucose testing?

The primary reason for using the gray tube for glucose testing is that it contains sodium fluoride, which acts as a glycolytic inhibitor. This means that it inhibits the metabolism of glucose by the blood cells, thereby preserving glucose levels in the sample during the time between the blood draw and analysis.

Sodium fluoride is especially important in glucose testing because glucose can be rapidly utilized by red blood cells and other cells in the blood, leading to decreased glucose levels in the sample if not properly preserved. By using the gray tube that contains sodium fluoride, laboratories can ensure more accurate glucose measurements, which is critical for diagnosing and monitoring conditions like diabetes.

The other options provide different functions or purposes for various additives in blood collection tubes, but they do not relate to glucose preservation in the same way that sodium fluoride does.