What color tube is used when collecting a blood sample to test for alcohol levels?

The correct choice for collecting a blood sample to test for alcohol levels is the gray tube. This tube typically contains a glycolytic inhibitor, such as sodium fluoride, which helps to preserve the glucose levels in the sample while preventing alcohol from being metabolized by the blood cells. By using a gray top tube, healthcare professionals can ensure that the alcohol concentration remains stable during transport and analysis, leading to accurate test results.

The other options do not serve this specific purpose: the blue tube is primarily used for coagulation studies, the red tube is often used for serum tests, and the green tube is typically used for tests that require heparin as an anticoagulant. Each of these tubes has specific additives that may interfere with alcohol tests, thus making the gray tube the preferred choice for accurate alcohol level determination.