Mixing Studies
March 4th, 2023
On this page:Correction of PT/INR with MixingNon-Correction of PT/INR with MixingCorrection of APPT with MixingNon-Correction of APTT with Mixing
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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