When should the gray top tube be filled?

The gray top tube is specifically designed for tests involving glucose or lactate. This tube contains additives such as sodium fluoride, which acts as a glycolytic inhibitor, preventing the breakdown of glucose by any cells that may be present in the sample. By doing so, it ensures the accuracy of glucose measurements, especially in situations where the sample might not be processed immediately.

When collecting blood samples for glucose testing, filling the gray top tube is particularly essential to maintain the integrity of the sample and obtain reliable results. Lactate levels are also measured using this tube, as the fluoride additive inhibits lactate consumption by anaerobic bacteria in the sample.

The other options pertain to tests that require different types of tubes. For example, liver function tests and routine CBC tests are typically collected in different tubes that are better suited to the specific requirements of those tests, such as serum or EDTA tubes. Thus, the correct answer reflects the appropriate usage of the gray top tube in laboratory testing.