What color is used to identify blood collection tubes containing citrate?

• A. Green
• B. Light Blue
• C. Red
• D. Gray

Answer: (B)

Light blue top identifies tubes that contain citrate. Sodium citrate acts as an anticoagulant by binding calcium, which stops clotting in the tube and preserves the plasma for coagulation testing (such as PT and aPTT). Accurate clotting results require the correct citrate-to-blood ratio, so tubes must be filled to the specified volume; underfilling alters this ratio and skews results. After drawing, gently invert to mix and process to obtain plasma. The color coding helps labs pick the right tube for coagulation studies, while other colors indicate different additives or purposes (green for heparin, red for no additive/serum, gray for fluoride/oxalate).