What is the additive in a red plastic tube?

• A. Gel separator
• B. Sodium citrate
• C. Clot activator
• D. EDTA

Answer: (C)

The additive in a red plastic tube is indeed a clot activator. This type of tube is designed to facilitate the coagulation of blood, which is essential for obtaining serum specimens after the blood has clotted. The clot activator works by providing a surface area that accelerates the clotting process, allowing the blood cells to separate from the serum more efficiently once centrifuged.

In contrast, the gel separator is typically found in serum separator tubes that have a gel barrier to prevent the serum from interacting with the cells after centrifugation, which is not the purpose of red plastic tubes. Sodium citrate is an additive for blue-top tubes used in coagulation tests, as it binds calcium to prevent clotting. EDTA is found in lavender-top tubes and acts as an anticoagulant by binding to calcium, but it does not play a role in red plastic tubes. Therefore, the presence of a clot activator in red plastic tubes is crucial for producing serum samples for testing.