The gray topped tube is usually drawn for which test?

The gray-topped tube is specifically designed for tests that require the measurement of glucose and is particularly important for storing blood specimens that need to be tested for glucose levels. It typically contains sodium fluoride, which acts as a glycolytic inhibitor, preventing the breakdown of glucose by the cells in the blood sample. By inhibiting glycolysis, the gray-topped tube ensures that the glucose levels measured in the laboratory reflect the actual concentration present at the time of the draw, providing accurate results for glucose testing.

While the other tests listed may be important in their own right, they do not require the specific additives found in the gray-topped tube. Electrolytes, liver function, and thyroid function tests are generally performed using different types of collection tubes that are optimized for those particular assays, which do not have the same need for glucose preservation. Thus, the gray-topped tube stands out as the choice associated with glucose testing.