The citrate anticoagulant used for coagulation testing is contained in tubes with which lid color?

• A. Green lid
• B. Blue lid
• C. Lavender lid
• D. Red lid

Answer: (A)

Blue-lid tubes contain sodium citrate, which acts as the anticoagulant used for coagulation testing. Sodium citrate works by binding calcium, preventing blood from clotting so plasma can be collected and analyzed for clotting factors (like PT and aPTT). For accurate results, these tubes are filled to the correct blood-to-anticoagulant ratio (about 9:1) and gently inverted to mix, then processed to obtain platelet-poor plasma. Other common lid colors map to different additives—green lids have heparin, lavender lids have EDTA, and red lids are for serum without anticoagulant—so blue-lid tubes are specifically the citrate tubes used for coagulation studies.