Michael Laposata, M.D., Ph.D. Director of Clinical Laboratories ...

1 Check in Box for Prolonged PTT PanelInitiates Use of This Test Selection AlgorithmProlonged PTT EvaluationDegrade heparin in sample and repeat PTT -if the PTT normalizes, heparin is the causePTT mixing study (1:1 mix ofpatient:normal plasma)PTT NormalizesPTT remains prolongedFactor deficiencymeasurefactors VIII, IX,XI, and XIIInhibitor, most commonly Lupus anticoagulant;may be a Factor VIII inhibitorif PTT mixing study first normalizes andthen becomes prolongedPerform tests for specific inhibitorssuggested by results of PTT mixing study