Which additive is present in the light blue top tube?

• A. 3.8% sodium citrate
• B. Potassium oxalate
• C. 3.2% sodium citrate
• D. Heparin

Answer: (C)

Light blue top tubes are used for coagulation studies and contain sodium citrate as the anticoagulant. Sodium citrate works by chelating calcium, preventing clotting while preserving the coagulation factors for accurate tests like PT and aPTT. The standard concentration for this tube is 3.2% sodium citrate, which ensures the proper 9:1 blood-to-anticoagulant ratio needed for reliable results. That’s why the correct additive is 3.2% sodium citrate. Potassium oxalate is associated with gray tubes for glucose testing, and heparin is used in green (and some other) tubes for chemistry tests, not in light blue. The 3.8% sodium citrate is not the typical format for routine coagulation testing in this tube.