Which color tube is drawn last in the standard order of draw?

• A. Pink
• B. Lavender
• C. Median
• D. Gray

Answer: (D)

In the standard draw sequence, each tube’s additive is matched to preserve the integrity of the tests and prevent carryover from one tube to the next. The gray tube is drawn last because it contains sodium fluoride, a glycolysis inhibitor, often with potassium oxalate as an anticoagulant. If its additive were introduced earlier, it could interfere with results of tests in the other tubes or become a source of carryover contamination. Placing the gray tube last isolates its glycolysis-inhibiting effects to the glucose-testing specimen and helps ensure accurate glucose measurements. Other colored tubes in the list are used for different tests with their own additives, and they’re collected earlier in the sequence.