Phlebotomy Technician Practice Exam (NCPT/CPT) 2025 - Free Phlebotomy Practice Questions and Study Guide

The correct order of draw when using a winged infusion set, often referred to in medical settings as a "butterfly" needle, is significant to avoid cross-contamination of additives from one tube to another, which can compromise test results.

In this scenario, the order starts with the light blue top tube, which contains sodium citrate. It is essential for coagulation tests, such as the Prothrombin Time (PTT), and should always be drawn first to prevent any contamination of its anticoagulant properties by additives from other tubes.

Following this, the lavender top tube is used for hematology tests, including the complete blood count (CBC). This tube contains EDTA, an anticoagulant that is compatible with the requirements for CBC testing and is drawn after the light blue tube to ensure that no factor from other tests interferes with its results.

Lastly, the serum separator tube (SST), which is often used for chemistry panels, is drawn last. This tube contains gel or clot activators and is specifically designed to separate serum from cells after centrifugation, making it critical that it is not contaminated by other tubes.

The careful adherence to this order helps ensure that test results are valid and reliable, making the identified