What is the purpose of a red top tube in the lab?

• A. Serum collection; plain tube with no additive or clot activator
• B. Contains clot activator
• C. Contains anticoagulant for whole blood tests
• D. Plasma collection with EDTA

Answer: (A)

The main idea is how tube additives determine whether you get serum or plasma. A red top tube is a plain, nonadditive tube with no clot activator and no anticoagulant. When blood is drawn into it, it is allowed to clot, and after separating by centrifugation the liquid obtained is serum. Serum is the fluid left after the clotting factors have been used up in forming the clot, with no fibrinogen present. So this tube is used when the test requires serum without any additive interference.

Tubes with clot activators would speed up clotting but still yield serum, while tubes with anticoagulants prevent clotting and produce plasma (not serum). A tube designed for plasma collection with EDTA would use EDTA to prevent clotting, again yielding plasma rather than serum.