When drawing from a difficult vein, which tube should be filled last?

The correct answer is the lavender top tube. When dealing with a difficult vein for blood collection, the order of draw is crucial in preventing contamination and ensuring accurate test results. The lavender tube contains EDTA, an anticoagulant that is sensitive to contamination from other additives. By filling this tube last, you reduce the risk of carryover from other tubes that may contain different additives, particularly those that might alter coagulation results.

In the order of draw, the lavender top tube, which is used for hematology tests like complete blood counts, is typically drawn after the clotting tubes (like red and light blue). This is to ensure that the specimen collected in the lavender tube is not affected by additives from previous tubes. As a result, drawing the lavender tube last ensures that it arrives at the lab with the highest integrity.