19/09/2025
🌺The Mixing Test for PT and aPTT 🌺
🌺 performed to investigate the cause of bleeding tendency or impaired hemostasis when Prothrombin Time (PT) or Activated Partial Thromboplastin Time (aPTT/PTT) is found to be prolonged.
(⚠️ If PT or aPTT is within the normal range, a mixing test is not indicated.)
👉 Therefore, before performing a mixing test, PT or aPTT should first be confirmed as prolonged.
🌺Mixing Test (PT & aPTT)🌺
🍁Principle
🔸Mix patient plasma : normal pooled plasma = 1:1
🔸Measure PT/aPTT immediately and after incubation at 37°C for 60 minutes
🍁Interpretation
🔸Corrected → Factor deficiency
(e.g., aPTT decreases >50% or returns to reference range)
🔸Not corrected → Inhibitor(e.g., lupus anticoagulant, specific factor inhibitor)
🔸Immediate correction but prolonged after incubation → Time-dependent inhibitor
(e.g., anti-Factor VIII)
🔸Persistent non-correction → Common in lupus anticoagulant, nonspecific inhibitors, or heparin contamination
🍁Cautions
🔸Possible interferences: heparin contamination, incorrect blood:citrate ratio, hemolyzed/lipemic/icteric samples, or improperly prepared NPP
🍁Next steps
🔸If factor deficiency is suspected → Perform factor assays (II, V, VII, X for PT; VIII, IX, XI, XII for aPTT)
🔸If inhibitor is suspected →
*** For lupus anticoagulant: perform specific tests (dRVVT, LA-sensitive aPTT, mixing + confirm procedures per guidelines)
*** For specific factor inhibitors: perform Bethesda assay to measure inhibitor titer (e.g., anti-FVIII)
*** Always interpret in conjunction with medication history (e.g., heparin, DOACs) and clinical context (liver disease, DIC, vitamin K deficiency)
💐 Summary💐
🔸Correction → Factor deficiency
🔸No correction → Inhibitor
🔸Immediate correction → prolonged after incubation → Time-dependent inhibitor 🥰
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