Comparing Methods of Establishing the aPTT Therapeutic

Despite over 50 years of clinical experience with hep-arin therapy for thromboembolic disorders, an ideal approach to measuring its anticoagulant activity, although widely sought, has not been established. Both the Ameri-can College of Chest Physicians and the College of Ameri-can Pathologists recommend the establishment of a hep-arin concentration – derived therapeutic range (HCDTR) for the activated partial thromboplastin time (aPTT).1,2 An HCDTR is defined as the range of aPTT times which corre-spond to heparin concentrations of 0.2–0.4 µ/mL by pro-tamine titration or 0.3–0.7 µ/mL by an anti-factor Xa assay. To accomplish this, the aPTT and heparin concentration should be simultaneously determined in blood samples tak