Advanced Phlebotomy Practice Test

Which tube contains EDTA and is used for hematology tests such as CBC, Hgb, and Hct?

Gray Tube — Na Fluoride/K Oxalate Lavender Tube — EDTA SST (Tiger Top) — No additive Red Tube — No additive

Correct Answer:

Lavender Tube — EDTA

Explanation:

The main idea is that hematology tests require an anticoagulant that keeps the blood from clotting while preserving the cells for accurate counting. The lavender-top tube contains EDTA, which binds calcium and prevents coagulation, so the sample stays as whole blood with intact cells. This preservation of cellular morphology is essential for reliable CBC results, including hemoglobin concentration and hematocrit. The other tubes serve different purposes: gray-top tubes have fluoride/oxalate for glucose testing and aren’t ideal for hematology; SST tubes are serum tubes with no additive or gel and require clotting, which alters the cells; red-top tubes are plain serum tubes after clotting, also not suitable for CBC.

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