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Coagulation
 
 

Overview

Mixing studies are used to determine the cause of prolonged PT/INR and/or APTT.
When performing mixing studies, the patient's plasma is mixed 50:50 with control plasma, and then the PT/INR or APTT is measured.
  • Interpretation

  • If the APTT or PT/INR is initially elevated but becomes normal when control plasma is added, this suggests that there is factor deficiency as the cause of coagulopathy.
  • If the APTT or PT/INR remains elevated despite addition of control plasma, this suggests that there is an inhibitor present in the sample.

Correction of PT/INR with Mixing

If the PT/INR is initially elevated but becomes normal when control plasma is added, this suggests that there is factor deficiency as the cause of coagulopathy.
This occurs commonly in the setting of warfarin or vitamin K deficiency, however may occur in the context of deficiencies affecting multiple pathways.
  • Causes of PT/INR Correction with Mixing

  • Warfarin
  • Vitamin K deficiency
  • Congenital factor deficiency
  • Disseminated intravascular intracoagulation
  • Liver failure

Non-Correction of PT/INR with Mixing

If the PT/INR remains elevated despite addition of control plasma, this suggests that there is an inhibitor present in the sample.
  • Causes of PT/INR Non-Correction with Mixing

  • Factor IIa inhibitors (e.g. dabigatran)
  • Excess heparin in the tube

Correction of APPT with Mixing

If the APTT is initially elevated but becomes normal when control plasma is added, this suggests that there is factor deficiency as the cause of coagulopathy.
  • Causes of APTT Correction with Mixing

  • Congenital factor deficiency
  • Von Willebrand disease
  • Disseminated intravascular coagulation
  • Supratherapeutic warfarin

Non-Correction of APTT with Mixing

If the APTT remains elevated despite addition of control plasma, this suggests that there is an inhibitor present.
This occurs commonly in the context of heparin, though may also occur with antiphospholipid syndrome.
  • Causes of APTT Non-Correction with Mixing

  • Heparin
  • Factor IIa inhibitors (e.g. dabigatran)
  • Lupus anticoagulant
  • Specific factor inhibitors
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