Which color-coded tube contains sodium citrate?

• A. Green
• B. Sodium citrate
• C. Blue
• D. Orange

Answer: (B)

In this testing area, tube color tells you the additive inside. Sodium citrate is used as an anticoagulant to preserve clotting factors for coagulation testing, and the tube color designated for sodium citrate is blue. It works by binding calcium, which stops the clotting process so you can obtain plasma for tests like PT and aPTT. To ensure accuracy, collect the correct amount of blood up to the marked line and mix gently by inverting the tube. Other color tubes have different additives (for example, green tops contain heparin; orange tops may have a clot activator), but the blue-top tube is the one that contains sodium citrate.