In the absence of blood cultures, what is typically the second tube drawn in the standard order of draw?

• A. Lavender top tube
• B. Light blue top tube (sodium citrate) for coagulation testing.
• C. Gray top tube
• D. Red top tube

Answer: (B)

The main idea is why a citrate-containing tube is drawn early for coagulation testing. The light blue top tube holds sodium citrate, an anticoagulant that binds calcium to prevent clotting, which is essential for accurate coagulation studies like PT/INR and aPTT. Because the test requires plasma with a precise blood-to-anticoagulant ratio, this tube is placed early in the draw sequence and is drawn in a fixed position after any blood-culture bottles. When blood cultures aren’t being collected, the light blue tube remains the appropriate early tube to obtain the necessary coagulation plasma, avoiding contamination from other additives found in different tubes. In short, the light blue top tube is used for coagulation testing and is positioned early in the order to preserve sample quality and test accuracy.