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🔬Lab & Specimen Handling

What is a blue top tube?

A blue top tube contains sodium citrate and is used for coagulation tests including PT, INR, and PTT.

Sodium citrate prevents coagulation by binding calcium. The 9:1 ratio of blood to citrate is critical — under- or over-filled blue top tubes produce inaccurate coagulation results. This tube must be filled to exactly the marked line.

Common tests using blue top tubes:

  • Prothrombin time (PT) and International Normalized Ratio (INR)
  • Partial thromboplastin time (PTT/aPTT)
  • Fibrinogen
  • D-dimer
  • Factor assays
  • Platelet function assay (PFA-100)

    • Invert 3–4 times gently after collection. Centrifuge within 4 hours.

    What is an EDTA tube?How much blood is drawn per test?

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