_________ shields blood from the glass of the collection tube and prevents it from clotting.

• A. Seal
• B. Cap
• C. Anticoagulant
• D. Gel Separator

Answer: (C)

Anticoagulant is the additive in the tube that prevents blood from clotting. It works by interfering with the clotting cascade—often by binding calcium or inhibiting certain clotting factors—so blood remains fluid even when it contacts the glass interior of the tube. A seal or cap only keeps the tube closed; it doesn’t affect clotting. A gel separator helps after processing to keep plasma separate from cells and doesn’t prevent clotting during collection. Therefore, the anticoagulant best fits the description of shielding the blood from clotting.