What is the rationale for the standard order of draw?

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The order of draw exists to prevent additives from one tube contaminating another and to let serum samples clot properly. Some tubes contain anticoagulants or other additives that can alter test results if carried into subsequent tubes. If a tube with an additive is drawn before serum tubes, that additive can contaminate the serum sample and interfere with clot formation, compromising many tests. By following the standard sequence, you minimize cross‑additive interference and ensure that serum tubes clot normally, giving accurate chemistry and serology results. This isn’t about patient comfort, processing speed, or labeling—those aren’t addressed by the draw order.