When collecting a Prothrombin Time (PT) test, a Complete Blood Count (CBC), and Fasting Blood Sugar (FBS), what is the correct order of draw?

The order of draw is essential in phlebotomy to prevent cross-contamination of the different additives present in the collection tubes, which can affect test results. The correct sequence for drawing blood, especially when collecting a Prothrombin Time (PT) test, a Complete Blood Count (CBC), and Fasting Blood Sugar (FBS), is to start with the light-blue tube, followed by the lavender tube, and finally the gray tube.

The light-blue tube typically contains sodium citrate, which is an anticoagulant used for coagulation tests such as the PT. It must be drawn before tubes that contain additives that could interfere with the coagulation process. Next, the lavender tube, which is used for hematological tests like CBC, contains EDTA as an anticoagulant. Since EDTA does not affect coagulation tests, it is appropriate to collect it after the light-blue tube. Finally, the gray tube is used for glucose testing, often containing additives like potassium oxalate and sodium fluoride, which inhibit glycolysis and preserve glucose levels; thus, it is drawn last to avoid contamination.

Following this specific order ensures that each test is performed accurately without interference from the additives of subsequent tubes.