According to the CLIA order of draw, which tube is filled last?

In the context of the CLIA order of draw, the lavender top tube is filled last to prevent contamination of the additive present in the tube. The order of draw is established to minimize the risk of additive carryover from one tube to another, which can adversely affect laboratory test results.

The lavender top tube contains EDTA, an anticoagulant that binds calcium and prevents blood clotting, making it essential for certain hematology tests. If it were to be filled earlier in the draw sequence, there could be a risk that residual additives from previously drawn tubes, especially those with gel or clot activators, might interfere with its anticoagulant properties and compromise test accuracy.

By ensuring that the lavender tube is filled last, the integrity of the sample is preserved, allowing for reliable hematological analysis. This careful attention to the sequence is a fundamental aspect of phlebotomy practice, which emphasizes the importance of proper protocols in obtaining and handling blood samples.