In the order of draw, which of the following tubes is typically filled last?

The typical order of draw for blood collection is designed to prevent cross-contamination of additives between tubes. In this order, the gray tube is generally filled last. This is because gray tubes contain additives such as sodium fluoride and potassium oxalate, which are used for glucose testing and can interfere with the tests performed in other tubes if filled earlier.

By filling the gray tube last, it minimizes the risk of contamination from other tubes that may contain different additives, ensuring accurate test results. The presence of additives in the other types of tubes—like anticoagulants in the lavender and green tubes—make them more susceptible to contamination if drawn beforehand.

Thus, filling the gray tube last is crucial for maintaining the integrity of the samples collected, particularly for glucose measurement and other tests that require the specific conditions that the gray tube’s additives provide.