Lavender top blood tube contains which additive?

• A. Sodium fluoride
• B. Citrate
• C. Heparin
• D. EDTA

Answer: (D)

Lavender-top tubes use an anticoagulant that chelates calcium, preventing clotting and preserving blood cell morphology for hematology tests. This additive is EDTA, usually as potassium EDTA, which keeps the sample in a whole, unmixed state ideal for complete blood counts and related analyses. The reason this works is EDTA binds calcium, a mineral required for the clotting cascade, so the blood doesn’t coagulate.

Other additives have different roles: sodium fluoride mainly inhibits glycolysis rather than acting as an anticoagulant for CBC work; citrate binds calcium and is used in coagulation studies (in light blue tubes); heparin is another anticoagulant used for plasma chemistry tests (often in green tubes). So the lavender top is specifically chosen for EDTA to best preserve cells for hematology.