JULY 20, 2009

Topic: Improved Prothrombin Time (PT) Testing Method

Summary: Westcliff Medical Laboratories (WML) is switching to a new, more specific and sensitive reagent of prothrombin time (PT) (test code: 1201) effective July 20, 2009. The reference interval for PT will be slightly changed.

Key Facts: The new PT reagent (human recombinant thromboplastin) exhibits an improvement in sensitivity to the effects of oral anticoagulant therapy. Sensitivity of thromboplastin is measured by its ISI. Thromboplastins with low ISIs are more responsive or "sensitive." The new reagent has an ISI of 1.0 compared with 1.9 for the previous reagent meaning that the new reagent provides a more linear and sensitive prothrombin assay.

Reference Range Changes: The reference interval for prothrombin time will change to 10.0 - 13.0 seconds from the old range of 11.0 – 13.0 seconds.

The American Heart Association suggested the following International Normalized Ratio (INR) therapeutic ranges:

Patients stabilized on oral anticoagulant: 2.0 - 3.0

Patients with recurrent systemic embolism, mechanical prosthetic valves, or post acute myocardial infarction: 2.5 - 3.5

Collection Process and Transport Process: The collection and transport requirements for prothrombin time specimens have not changed. You may submit a full citrated whole blood tube (blue top) or frozen plasma.

In-lab turnaround Time: The assay is performed seven days per week and is available STAT.

If you have further questions please contact your WML sales representative or the client service department at 800-373-9505.