Sodium Citrate Vacutainer

These are the blue-top blood collection tubes mainly used for coagulation tests. Quick, clean, and very specific in purpose. Key details: Additive: Sodium citrate (usually 3.2% / 0.109 M; sometimes 3.8%) Function: Binds calcium to prevent clotting (reversible) Blood : additive ratio: 9 : 1 → tube must be filled to the mark for accurate results Common tests: PT / INR APTT D-dimer Fibrinogen Coagulation factor assays