CPT (Certified Phlebotomy Technician) Practice Exam

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What chemical additive is in a green tube?

Lithium Heparin
Sodium Heparin
Sodium Citrate
Silicone

The correct answer is: Sodium Heparin

The correct answer is lithium heparin. A green-top tube typically contains an anticoagulant, which is a substance that prevents blood from clotting and allows for the collection of plasma. Lithium heparin is a commonly used anticoagulant in green tubes, effectively inhibiting the clotting process by activating antithrombin III. In laboratory settings, lithium heparin is preferred because it does not interfere with many tests and allows for accurate results, especially for blood chemistry tests. The use of lithium instead of sodium is beneficial in certain tests to avoid artifacts caused by the presence of sodium. While there are other types of heparin and additives, lithium heparin specifically is what is widely recognized for green-top tubes in clinical practice. Sodium citrate, another anticoagulant, is used in light blue tubes. Silicone is not an additive used for anticoagulation but is often a coating on certain containers.