In coagulation testing, which anticoagulant is typically used in tubes with a green lid?

• A. Sodium citrate
• B. EDTA
• C. Heparin
• D. Oxalate

Answer: (A)

The main idea is that tube color indicates the anticoagulant used and this affects which tests the blood sample is best suited for. Green-lid tubes contain heparin (usually lithium or sodium heparin), which prevents clotting by inhibiting certain clotting factors and is commonly used for plasma chemistry studies and rapid testing. For coagulation testing like PT and aPTT, citrate is preferred because it binds calcium and keeps the blood fluid until testing, at which point calcium is restored to start the clotting reaction in a controlled way. Citrate is typically found in blue-top tubes, not green-top. So, in standard practice, the green-lid tubes use heparin, not sodium citrate.