plasma mixing studies

Introduction

A set of tests in which the patient's plasma is mixed with plasma from a healthy individual or with pooled plasma.

Indications

• coagulation factor deficiency
• coagulation factor inhibitor

Principle

• addition of normal plasma to the patient's plasma will correct a deficiency in a coagulation factor, whereas will have less if any effect on a coagulation factor inhibitor
• the PT may correct initially after mixing, but not after 1 hour of incubation

* excess phospholipid is added to the patient's plasma & the aPTT corrects is consistent with antiphospholipid syndrome

Interpretation

• mixing studies correct PT & aPTT for
  • hepatic cirrhosis
  • vitamin K deficiency
  • disseminated intravascular coagulation (DIC)
  • von Willebrand disease including acquired von Willebrand disease
  • hemophilia
• aPTT does not correct for coagulation factor inhibitor
  • acquired hemophilia A (factor VIII inhibitor)
• correction of aPTT without correction of PT (after incubation) suggests inhibitor of coagulation factor VIIA
• 'correction' is an ambiguous term
  • complete correction of aPTT would imply aPTT < 35 seconds
  • a correction of aPTT from 85 seconds to 48 seconds or 90 seconds to 45 seconds is only a partial correction & is consistent with a coagulation factor inhibitor

More general terms

• clinical coagulation test