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, which is the chemical additive found in green-topped blood collection tubes. Lithium heparin acts as an anticoagulant, preventing blood from clotting during the collection process. This allows for accurate measurement of various blood parameters, particularly in tests that require plasma samples. In addition, lithium is preferred over sodium for certain serum tests, as it minimizes interference with some assays and provides more stable preservation of the blood sample. The use of heparin as an anticoagulant also allows for rapid processing of samples, which is essential in many clinical settings. While sodium heparin is indeed another anticoagulant, it is commonly associated with other colored tubes, such as the light green or green-gray (tiger) tubes. Sodium citrate, found in blue-topped tubes, is used primarily for coagulation tests, while silicone is not an anticoagulant but a lubricant that helps the blood flow smoothly without affecting the sample in collection tubes.