Certified Phlebotomy Technician I (CPT1) Full Practice Test 2026

The lavender top tube contains EDTA (ethylenediaminetetraacetic acid) as its additive. EDTA is an anticoagulant that works by binding calcium in the blood, thus inhibiting the coagulation process. Because of its ability to preserve cellular components and prevent clotting, the lavender top tube is primarily used for hematology tests, such as complete blood counts (CBC). The effectiveness of EDTA in maintaining the integrity of blood samples makes it a vital additive in certain laboratory analyses.

Other additives listed, such as sodium citrate and heparin, serve different purposes. Sodium citrate is primarily used in light blue top tubes for coagulation studies, while heparin, an anticoagulant, is found in green top tubes and serves a different function in managing blood sample processing. Serum separator gel, which is used in gold or red top tubes, allows for the separation of serum after centrifugation but does not prevent clotting in the same manner as EDTA. Each additive is specifically selected based on the desired laboratory analysis, highlighting the importance of understanding their distinct roles.