What additive is in a light blue top tube and which tests use it?

• A. Sodium citrate; used for coagulation tests such as PT/INR and aPTT.
• B. Sodium fluoride; used for glucose testing
• C. Sodium citrate; used for lipid profiling
• D. EDTA; used for CBC

Answer: (A)

The main idea here is recognizing what additive in a light blue top tube and what tests rely on it. Light blue tubes contain sodium citrate, an anticoagulant that binds calcium to keep blood from clotting. This preserves the coagulation factors, which is why these tubes are used for coagulation studies such as PT/INR and aPTT. For these tests, the accurate clotting time depends on the correct blood-to-anticoagulant ratio, so proper filling and mixing are crucial.

Sodium fluoride is used with gray-top tubes to preserve glucose, not for coagulation testing. Sodium citrate isn’t typically used for lipid profiling, which generally uses serum from red or gold/SST tubes. EDTA, found in lavender-top tubes, is used for CBCs, not light blue tubes. So the additive in a light blue top tube is sodium citrate, and it’s used for coagulation testing like PT/INR and aPTT.