Which position in the order of draw should the light blue be collected?

Which position in the order of draw should the light blue be collected?

• A. Third
• B. First
• C. Second
• D. Fourth

Answer: (C)

The main idea here is that coagulation tests require a precise blood-to-anticoagulant balance and must be drawn in a sequence that minimizes contamination from other tube additives. The light blue top contains sodium citrate, which binds calcium to prevent clotting, and it must be collected in a position that preserves this balance and avoids carryover from other additives. By drawing it second—after the sterile culture tubes to protect culture integrity but before tubes that contain EDTA or heparin—the sample is least likely to be contaminated by other anticoagulants. This helps ensure accurate PT and aPTT results and the correct 9:1 blood-to-anticoagulant ratio. Drawing it later increases the risk that additives from subsequent tubes could contaminate the sample and skew coagulation measurements, which is why it’s positioned second in the order of draw.

The main idea here is that coagulation tests require a precise blood-to-anticoagulant balance and must be drawn in a sequence that minimizes contamination from other tube additives. The light blue top contains sodium citrate, which binds calcium to prevent clotting, and it must be collected in a position that preserves this balance and avoids carryover from other additives. By drawing it second—after the sterile culture tubes to protect culture integrity but before tubes that contain EDTA or heparin—the sample is least likely to be contaminated by other anticoagulants. This helps ensure accurate PT and aPTT results and the correct 9:1 blood-to-anticoagulant ratio. Drawing it later increases the risk that additives from subsequent tubes could contaminate the sample and skew coagulation measurements, which is why it’s positioned second in the order of draw.