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At present, we are using the proposed therapeutic range for monitoring unfractionated heparin therapy which is the aPTT ratio of 1.5-2.5. However, the aPTT value is influenced by reagents and methods of detection. The College of American Pathologists and the American College of Chest Physicians recommended that site-specific validation of heparin therapeutic range should be established. The aim of this study was to determine the appropriate therapeutic range of unfractionated heparin therapy of our aPTT system by ex vivo study. For comparison, two other commercial reagents were also determined to observe the differences. Blood samples were drawn from 21 healthy blood donors who were not taking any medication and from other 24 patients suffering from either arterial or venous thrombosis, receiving continuous intravenous infusion of unfractionated heparin without concomitant oral anticoagulant therapy. Correlation coefficients between aPTT ratios and plasma heparin concentration varied between 0.722 (Actin FSL) to 0.817 (Actin FS). Calculated therapeutic ranges of aPTT ratios corresponding to the heparin level of 0.29 - 0.47 U/ml were 1.8 - 2.5, 1.9 - 2.5 and 2.7 - 4.6 for Actin FS, Actin FSL and Pathromtin SL, respectively. Therefore, the appropriate therapeutic range of our system obtained from this study might be aPTT ratio between 1.8 and 2.5 which is very closed to the ratio that we are using now.
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