At midday on 12/17/02, the laboratory will be changing to a new Coagulation instrument and different reagent lots, affecting the normal ranges of Prothrombin Time (PT), Activated Partial Thromboplastin Time (aPTT), Fibrinogen (FIBG), and the Thrombin Time (TT).

PT Reagent Lot Change: The reference range will change to 9-12 seconds and the mean of the reference range is 11 seconds. The international sensitivity index (ISI) is 1.0. There will be no impact of this change on the monitoring of oral anticoagulation.

aPTT Reagent Lot Change: The reference range will be 24-33 seconds and the mean of the reference range is 29 seconds.
Because of the significant variability in response of the aPTT reagent systems to heparin, twenty-six patient specimens with heparin levels of 0.3-0.7 U/ml were evaluated by an Anti-factor Xa method. The mean of this group of specimens is 60 seconds. The mean of the published therapeutic range for heparinization of 1.5-2.5 times the mean of the reference range yields values of 44-73 seconds with this reagent. Based on our studies of heparin responsiveness, this is a reasonable target range to use with this reagent when treating uncomplicated venous thromboembolism. If you have any questions concerning this change, please contact the Hemostasis & Thrombosis Laboratory at 6-3573.

Fibrinogen Reference Range Change: The new reference range will be 203-390 mg/dl.

Thrombin Time Reference Range Change: The new reference range will be 15-21 seconds.

Questions can be directed to Nancy Rosenthal, MD, Director of Hematopathology at 384-8751.